In chess circles, a bad chess
player. Often, but not always, an opponent who is not only much worse than you, but actively pisses you off with poor sportsmanship, bad manners at the board (or online), or just general dumbassery.
Keep in mind, patzerism is relative. Everyone is a patzer to someone
better. A person who casually plays chess is a patzer to even someone with a basic knowledge of tactics. That person is a patzer to a decent club
player. The decent club
player is a patzer to the club champion. The club champion is a patzer to Alexandra Botez. Alex is a patzer to Levy Rozman. Levy is a patzer to even a mediocre
GM. Every other human being alive is a patzer to Magnus Carlsen, and Magnus is a patzer to Stockfish.