The picture that you change your profile picture to on a social network for your birthday. This is usually done the day before your birthday because it will be seen by more people than normal as they wish you a generic "happy birthday."
Friend: Come on, we're going to be late!
FB User: Almost done! I just need to change my picture to my birthday profile picture so that people think I'm fun and popular when they wish me a happy birthday!
A person who is obsessed with the Harry Potter franchise to the point of planning their entire life around the release of the next Harry Potter movie or book.
Friend 1: I'M DROPPING EVERYTHING TO GO TO THE MIDNIGHT PREMIERE OF HARRY POTTER AND THE DEATHLY HALLOWS TONIGHT!!
Friend 2: You are such a Harry Potthead.
Girlfriend: Hey, I'm really in the mood tonight, if you know what I mean...
Boyfriend: Not now, I'm watching all of the previous 6 Harry Potter movies before the new one opens!
Girlfriend: Why am I dating a Harry Potthead??