Am I a bad friend for choosing not to attend one of my best friend's birthday party?

One of my best friend's 15th birthday is coming up and she's planning a party. I'm really hesitant to go though. The reason for this is because all of the people she invited I either don't know or just really don't like, and there's also going to be alcohol. I know, I'm probably a freak for not wanting to drink. But she knows I hate alcohol, and forgive me but there is something distinctly unappealing about sitting around and watching 30 underage kids get drunk and have orgies in the corner. I know I'll be the only one not drinking, and because of this I just really don't want to go. The party isn't on the same day as her actual birthday so I'm thinking I'll probably do something then. Does this make me a bad friend ?