I managed to to tick off a guy who decided to make me a target, so when he started insulting me over and over, here's what i said: "Oh my, Its so nice to know you love me so much!"
One thing I like to do is when the target/idiot is on a tangent, I just say "keep going, I'm at half-mast". It usually makes my friends laugh, but it just pisses the troll off even more.