A teenage girl (aged 15 or 16, roughly) in front of me in the Co-op was wearing a crop-top and a pair of knickers only. Not bikini bottoms, not short shorts but cotton M & S midi style knickers. I didn’t say anything (none of my business and she probably wouldn’t have approved my sartorial choices either). If I had been her mother, seeing her before she left the house, I would have said that it looked unhygienic and wasn’t an appropriate way to go to the shops.
YABU: People of whatever age can dress how they like when they go to the Co-op.
YANBU: A mini-skirt or pair of shorts are a minimum requirement when you’re off to the shops.