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 certain people's outrage, but that doesn't include Steve, as he had been wanting to deck him for years.