While this can be classified as a malaprop (inadvertent substitution of a word with a strong phonetic similarity), it can also be considered a bona fide malaphor, mixing “nip it in the bud” (put a stop to something in its early development) and “kick in the butt” (forceful encouragement). I have heard this idiom misused often by younger people, so my guess is that it is probably a phrase that has mutated from the past generation (mine) to the current one. Another example is the phrase “buck naked”, mutating to the current “butt naked”. Still another is the word “moot” to “mute”, as in “that’s a mute point”. Am I correct, or am I just turning into a grouchy old man?
A big thanks to Judge Yvonne for sending this one in.