Mike Barnes is a one-time character in one story arc (and physically in only the first strip). He appears in Bury My Heart at Fun-Fun Mountain. He is a valedictorian at Peter's school.
Mike attracts Peter's attention and asks him when he and "that girlfriend of [his]" go out, if he calls it a "blind date" as a pun. Thus, Peter punches him in the nose, much to his disgust over the blood and certain people's outrage, but that doesn't include Steve, as he had been wanting to deck him for years.
Between the Monday and Tuesday strips of this story arc, he tells the principal, Mr. Krimpshaw, about this altercation, much to the latter's shock.