Let me start by pointing out that mangled expressions (as some people derisively call expressions that are distorted from their "original" idiomatic forms) abide in every variety of the English language. They aren't exclusive to Nigerian English.
In native varieties of the English language, some mangled expressions have become so popular and so widely used that they have acquired sufficient social prestige to constitute new standards. Examples are "first off" (which is the mangled form of "first of all"), "most everyone" (which is the distorted form of "almost everyone"), "out the window" (where the preposition "of" is dispensed with), etc.
It's not only the lexical properties of expressions that are often the victims of mangling; popular sayings and aphorisms are also routinely distorted by native speakers. For instance, the popular expression "blood, sweat and tears" is actually a distortion of Winston Churchill's famous wartime speech to the British nation. His exact words are: "blood, toil, tears, and sweat." The expression "a little knowledge is a dangerous thing" is a distortion of "a little learning is a dangerous thing."
Similarly, the expression "there is method in my madness" is a misquotation of a passage from Shakespeare's Hamlet where Polonius observes: "Though this be madness, yet there is method in't." Likewise, the expression "Water, water, everywhere, and not a drop to drink" is a misquotation of British Romantic poet Samuel Taylor Coleridge's line in Ancient Mariner. In it he writes: "Water, water, everywhere, nor any drop to drink."
But we have all got used to these misquotations - or are not even conscious of them as distortions in the first place - because they are committed by the most educated people in the English-speaking world, and have been passed down to us. So we in Nigeria are only adding to a list that is already too long, except that we do not enjoy the same privilege as native speakers of the English in having our own mutilations conferred respectability over time.
Our deviations are forever condemned to being socially stigmatized as aberrant because we lack the cultural and social capital of native speakers of the language. My object in pointing out the following popular mangled expressions in Nigerian English is not to ridicule them but to simply call attention to them.
1. "Be rest assured." The fixed English idiom that this Nigerian English expression apes is "rest assured." It means to be certain. But it is rare in Nigerian English for the expression to be rendered without the pointless and intrusive "be." The following sentence is an example of how this phrase regularly occurs in popular Nigerian English: "You should BE rest assured that I will not disappoint you." The "be" in the phrase is superfluous. Native speakers of the English language don't include it.
I can't locate the source of this distortion, except to point out that what grammarians call the habitual, uninflected "be" (that is, where the verb "to be" doesn't change form under any circumstance) occurs a lot in Nigerian Pidgin English (such as in the expression "I be don see am today," i.e., "I have seen him today"), in African-American Vernacular English (such as in the expression "she be mean to me," i.e., "she is mean to me") and in many English-based pidgins and creoles. I am tempted to argue that the addition of "be" before the idiom "rest assured" in Nigerian English is attributable to the influence of Nigerian Pidgin English. Or, perhaps, it is inspired by a false analogy from expressions like "be careful," "be nice," etc.
2. "I appreciate." When I lived in Nigeria, this expression was not part of the repertoire of popular speech. Its widespread use in contemporary Nigerian English must be the result of the relentless cross-border linguistic flows that the Internet has enabled. The phrase is clearly a poor mimicry of "I appreciate it," the alternative expression for "thank you" in America, Canada, Britain, and other native-speaker linguistic climes. Without the addition of "it," "this," or "that," the phrase can only mean that the speaker or writer habitually shows appreciation but for nothing in particular; it does not convey the sense that he or she is thankful or grateful for a specific thing. The first time someone said "I appreciate" to me in Nigeria, I couldn't resist asking "you appreciate what?" As you can probably tell, that expression drives me crazy!
3. "To be at the safer side." The Standard English idiom that this expression distorts is "to be on the safe side." It means to be cautious or safe - or to err on the side of safety or caution. This seems to me like a sloppy distortion because it violates two basic grammatical rules. First, "on" is the preposition that almost always co-occurs with the noun "side" when it signifies location (e.g. "he is on my side"). Second, the word "safer" is a comparative adjective and comparative adjectives are used only when two things are being compared. Plus, comparative adjectives always co-occur with the conjunction "than," except in situations where the comparison is apparent.
4. "He is in soup." The standard rendering of this idiom is "in the soup." Without the definite article "the," the expression would mean something other than its conventional idiomatic meaning, that is, in trouble or experiencing difficulty. "He is in soup" could mean that someone has literally fallen into a pot of soup. One of the characteristics of idioms is that their grammatical properties are often fixed and unchangeable. This quality is called grammatical fixity, as I've pointed out many times here.
Nigerian newspapers are clearly to blame for the mangling of this idiom. One of the rules of (daily) newspaper headline writing is that articles (i.e., the words "the," "a," and "an") should always be dispensed with. In line with this rule, copyeditors in Nigerian newspapers cast headlines about people being "in soup," which is perfectly legitimate. The problem is that the general populace has now adopted and internalized this "headlinese" as if it were conventional, everyday English.
5. "You cannot eat your cake and have it." Native speakers of the English language usually render this expression as "you cannot HAVE your cake and EAT it." The sense the expression conveys is that once you've eaten your cake, you can't have it again. I am the first to admit that this sounds rather illogical. I can have my cake and then eat it afterwards. But language, especially the English language, is not often governed by logic. The history of this idiomatic proverb particularly proves this point.
When the expression first appeared in the English language in 1564 in John Heywood's collection of English proverbs titled "A dialogue Conteinyng the Nomber in Effect of All the Prouerbes in the Englishe Tongue," it was rendered as "wolde you bothe eate your cake, and have your cake?" The modern form of the expression, where the "having" of the cake precedes the "eating" of the cake, started only in 1812, according to linguistic historians. So, in a way, Nigerians are more faithful to the original rendering of the expression than modern native English speakers. I call this the mangling of a mangled expression!
However, Nigerians also tend to substitute "cannot" in the expression with "can never." I hold Evi Edna Ogoli's 1980s hit song "You Can Never Eat Your Cake and Have It" responsible for this.
6. "More grease to your elbow." The correct form of this peculiarly British English expression is "more power to your elbow." It is used to praise people and wish them continued success in what they do. The expression came into British English by way of Irish English. Although it has lost currency in contemporary British English, it is still actively used in Australian, Indian, and Pakistani English. The usual form of the expression in American (and increasingly British) English is "more power to you!"
It is still a mystery to me why Nigerians have chosen to delete the word "power" from the expression and replace it with "grease." No other variety of the English language (except, perhaps Ghanaian English which shares so many similarities with Nigerian English) lubricates the expression with "grease." I once speculated that the mangling arose out of a false attraction to the expression "elbow grease," which means "hard work." But, upon deeper reflection, I am dubious of the plausibility of my own speculation particularly because the expression "elbow grease" is completely absent in Nigerians' everyday English. That leaves me to think that it's probably derived from the profusion of oil metaphors in our everyday speech as a consequence of our status as an oil-producing country. But why is the idiom not rendered as "more oil to your elbow" since oil is a more usual word than grease? Well, I don't know.
7. "In affirmative." The definite article "the" is an integral part of the lexical properties of the expression that signifies a "yes" reply. So it should read "in THE affirmative." In Nigerian English, especially in Nigerian media English, the article is almost always omitted.
8. "Benefit of doubt." The proper rendering of this expression in native varieties of the English language is "THE benefit of THE doubt." Notice that there is the article "the" before "benefit" and another before "doubt." Of course, the omission of the articles is not sufficient to confuse native speakers of English, but it does indicate insufficient proficiency in the language.
9. "Bite more than you can chew." The appropriate idiomatic form of this expression is "bite OFF more than you can chew." It means taking a challenge that is far greater than one's capabilities. However, I will admit that the omission of the "off" in the idiom is not peculiarly Nigerian. Many non-native speakers and writers also omit it.
10. "It doesn't worth it." This is a distinctly Nigerian mangling of the expression "it's not worth it." The error arises, I suspect, from misrecognizing the word "worth" as a verb when, in fact, it is an adjective in the sentence. If you won't say "she doesn't nice" because "nice" is an adjective, not a verb, you also can't say "it doesn't worth it" because "worth," like "nice," is functioning as an adjective in this expression.
11. "One hell of trouble." The fixed English phrase that this Nigerian expression derives from is "hell of a" (also informally rendered as "helluva" in creative mimicry of how the phrase is pronounced in informal spoken English). The indefinite article "a" always appears after the preposition "of" in the expression. So if a native speaker of the English language were to describe someone as troublesome using that expression, she would say "he is one hell of a lot of trouble," not "he is one hell of trouble."
12. "Complimentary card." This is the default expression in Nigerian English for what speakers of other varieties of English call "business card." As I noted elsewhere, this phrase has to be the most senseless usage error we have normalized, one that will leave even the most perceptive non-Nigerian English speaker irredeemably clueless.
The word "complimentary" simply means "free," that is, costing nothing (example: "the author gave me a complimentary copy of his new book"). So a "complimentary card" simply means a "free card." There is nothing in the phrase to suggest that it is signifying a card on which are printed a person's name, contact details, and business affiliation. I once thought that the phrase emerged probably out of a shortening of "complimentary business card." But this doesn't seem a reasonable assumption to make because the phrase will be superfluous since no one ever sells business cards in the first place. It only makes sense to describe something as complimentary if it is normally sold.