Approach him in a friendly manner and point out that she's really drunk. Suggest that you call her a taxi or find the friends that she came with. If you don't feel safe confronting the guy, find the friends she came with and let them know and ask them to check on their friend. Or you can cause a distraction by spilling something or creating a diversion. If you feel comfortable you can call out to him. Loudly saying something like, "Hey man, she's too drunk." will get other people to notice and might make the guy realize that what he is doing is wrong.