I work in club security 7 times / 10 times a girl is in a group, she twerking/shaking it, and you come up behind her friends will screen for her whether your attractive enough to be allowed. If she personally screens or is alone, she'll turn and glance to verify your worthy. If not she'll (or her and her friends) just turn around and dance away facing you, or flat out walk away. If you want to circumvent higher uncertainty, try to make eye contact beforehand or let her see you checking her out, if she smiles/licks her lips/makes a typical flirty woman move. You're more likely than not preapproved for grinding.
As long as your not overly aggressive and grabbing hips off top without going through any of the above processes you're good, of course as usual #handsomegang is exempt
