Running their moron mouth the whole time.
Setting up the pieces wrong (e.g bishops, knights, king and queen squares).
Starting with the board in the wrong orientation.
Accusing you of cheating when you capture en passant.
Continuing the game after a completely hopeless loss or position.
Calling the game “chest.”
Exposing their king to check and having to be told they can’t do that.
Not castling because they’re busy launching an attack from move 3
Taking every single exchange on the first move it’s available.
Fianchettoing their bishop and then throwing it away for a piece of garbage on the other end of the board.
Trying to play the whole game with their queen.
Actually having the audacity to try the scholar’s mate.
Putting their knight on the rim for no reason at all.
Blowing out their king-side pawn coverage to chase after a knight/bishop while both queens and all the other pieces are still on the board.
Spending the whole opening moving pawns and blocking their minor pieces from development in the process.
Playing only blistering fast games when they don’t have any board-vision intuition or idea how to play
…
That’s about all I can think of right now;)
.