Tamper with the software on your opponent's rangefinder to give him bogus readings. Fill the grooves of his clubs with glue. poke a hole in his driver head. Replace his ball with one of those exploding balls. Accidentally cough in his backswing. If he uses a push cart loosen the wheels so it falls apart and he has to carry. Make up rules and tell him he's breaking them. And don't forget to wish him luck before every single shot. Combine all that and you'll never lose