You ask them what they are doing in the Men's Room.

The girls laughter trails off into silence and you realize to your horror that you know some of them.

"What are you doing in the men's room?", you ask.

Erica, a tall thin brunette that you know, explains, "Um, today is supposed to be a women's only swim at the pool; and the ladies locker is locked and has a sign on it telling us to use the men's room."