Friends Carjacking You
Here's a fun little Easter Egg in GTA IV that I discovered the other day; Take a friend out to do an activity and when you take then home, park your car so the passenger door is blocked. As a result, they'll punch you out of the car so they can get out!
By the way, here's a video of it in action (Not mine):http://www.youtube.com/watch?v=A0iX51fDnZo&feature=related