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.
The condition known as Dick Buttkiss occurs in severely overweight men who are already experiencing a prolonged case of "flounder dick". The flounder dick is forced to migrate so far south that it eventually locates itself right up against your butthole- resulting in a Dick Buttkiss.