1.Your assassin henchman just wet his pants
2.The ancient red dragon you had just been fighting says "S**t, Iâ€™m out of here!" and flies away.
3.The bad guy just laughed evilly, and seven birds fell dead out of the sky.
4.The DM chuckles, and says "I spent seven hours rolling this guy up".
5.The bad guy burps, and a human toe flies out of his mouth.
6.The DM plays a tape of scary organ music, and starts talking like Boris Karloff.
7.The bad guy is dressed all in black, but has one of those little yellow smiley face buttons (DMs can be sooo sarcastic).
8.You point your wand of fire at him, and it melts.
9.The bad guy keeps Elminster in a cage, and occasionally pokes him with a fork.
10.After the battle, the only PC to survive is the one that stayed back in town with the flu.