if you want to sneak out, have a scavenger hunt. Plan this with people that AREN'T coming to your birthday party, and it can be a competition (with guy friends, etc.).
Or, go onto Yahoo! Movies, and check Coming Soon for movies that will be playing in February. You might see one that sounds fun to go see.
If you like the sound of going to get your nails done, look for a local hair dressers or spa that does that sort of thing. Book peds., mans., or maybe facials for every girl.
Order a pizza or two for back home, and rent some NEW movies.
Make sure you do stuff like just have a wild time, pump up the music, maybe grab a friend's bra outta her bag and throw it in the fridge.. stuff like that.
AND HAVE FUN!