a girl at a party who purposely stands out and expects you to supply her with gifts and alcohol.
Amber was obviously the birthday girl that night.
A person who has had so much alcohol that they pass out within a short time of partying. The gender of said partier does not matter, nor does it matter if it's the person's birthday or not. Basically being really, really fucked up.
1) A. Woah there, why are you carrying Jarrett out of the party already?
B. He went into birthday girl mode real quick tonight, sorry guys.
2) A. Hey Cody, nice win for the football team huh?
B. Hell yeah bro! Parties are going to be sick! I am definitely going birthday girl tonight.