Are "toothin' " and "puncha" a short form of something? Is something skipped to these words?
"Tootin'" is a slang term that can be two different things: it could be used to emphasize "tough," or it could be used to make Finn's song sound better. "Tootin'" is a very informal term and is not used often, so I do not recommend using it. "Puncha" here means "punch." "Puncha" is not a word in this sentence; it is just how this character is pronouncing "punch" in this scene. It can sometimes be used to mean "punch you," but since he says "yo" (meaning you) after "puncha," it just means "punch."