Snatch-Watch

To be on 'snatch-watch' is to assume or be assigned the responsibility of notifying a friend that her vagina is showing because her dress (which she knew was risky, pre-going out) has risen up.

A girl emerges from a cab. A second turns her legs to step out. The first girl alerts the second of her exposed lady parts. Sometimes by yelling "snatch-watch"

Girl 1: That's super cute. You have to wear it!
Girl 2: Fine. But you're on snatch-watch tonight.