Real Answer: Some do it when they're drunk because they have a curiosity they're only comfortable exploring after a few drinks lower their inhibitions. Others like the attention from the boys after they do it.

Another Possible Not So Fake Answer: To keep guys like Steve from hitting on them by appearing to be lesbians.

Not So Fake Reaction: Steve will hit on them anyway because in his mind all lesbians are actually bisexual and looking for a third. A third with some sweet cowboy boots.