I’m only guessing that these girls are drunk, because I can’t imagine a sober person willing to be dancing the Charleston in public. At least during this modern era. It looks like something a couple of girls, drunk from the open bar at a wedding, attempting to show off some moves. Not the “moves” I would be showing, but if it’s a couple of cute girls I can deal with watching them.
This is one of them nip slips where the camera was just at the right place, at the right time. She doesn’t appear to be wearing a trampy outfit or anything, so that nipple became visible at the same time this photo was snapped, by no real fault of her own, besides maybe not wearing a bra.