It depends on why they're laughing. If I don't know why, I'll scream at them until they tell me, or I poke them until they get fed up. If they're laughing at one of my jokes, then that's o.k. If they laugh at my misfortune, or someone else's, I go kick their butts. Most of the time, though, I laugh at myself anyway, usualy when I'm not, or something's not funny.