Simon Knott castled kingside, played Kh2, and then changed his mind and started marching his king over to the other side of the board!
When I did a similar maneuver against Weyerstrass he mated me as the king arrived, exhausted, on the queenside.
Edit: Game 3690130. Actually he didn't mate me, he just opened up the queenside before I could blink and made my king look foolishly exposed.