A word that pertains to someone or something that "kicks
butt".
However, recently, the word has devolved to be used as a noun, adjective, verb, and even an idiom. In
reality, buttkicker is simply the grammarically incorrect way of saying "kicks
butt".
Sam: When your friend tries to
make good roasts but then ends up failing: buttkicker.
Tom: STFU Sam you
degenerate that isn't how you say it.