It's a tail. That wags when you're happy.
Because I definitely need to give people an excuse to stare at my butt.
(True: When I went to a bridal show with My then-bride-to-be Sister the Lawyer, one of the men with a "Groom" sticker--who was holding hands with a woman wearing a "Bride" sticker, mind you--"accidentally" copped a feel of my butt. Dude, here's a hint: If you want to make it seem like an accident, DON'T FOLLOW THE CURVE.)