Me and my gf have a really close guy friend. All 3 of us would sometime hang out at my gf's place. What happen is that my gf has a tendency to wear very little when she is at home. Little as in just a dress like this Cascading Ruffle Dress over barely covering her bum with nothing under. Nothing as in no bra and pantie. So basically she was wearing like that even when he's here. What do I say to her to avoid her having these kinds of moment again? How can I stop it?