Wiping your anus when it does not immediately follow defecation. Such times may occur when you have a sweaty bum cleavage, you're worried something has dribbled out, or you simply didn't do a good job of wiping it in the first place.
A Vanity Wipe is nearly always accompanied by checking the toilet paper for streaks. It is often abbreviated to VW when discussed in a public place.
Friend #1: My arse crack is really fucking itchy
Friend #2: Go have a vanity wipe dude, it might sort you out