Antagonizing other people's girlfriends is great. It pisses the girlfriend off, pisses the guy off, and adds a small bit to the engulfing emptiness that is the soul of a single person. So at any and all opportunities, I choose friends' girlfriends as a target.
The other day, a friend asked me to hold his phone. WHAT A GENIUS. I of course immediately waited until his back was turned and texted his girlfriend "I think we should break up". In my defense, I put a few lines of blank text, and, out of sight unless you scrolled down, put "just kidding this is <my name>". Not my fault if the girl can't maintain basic reading comprehension. Needless to say she freaked out and called him relentlessly, and guess who kept hanging up on her?
He didn't care much for my antics when he caught the backlash later, but as a great man once said, if he can't take a joke, fuck him.