I'll second thongs! all wrong imo, even when only that top bit is visible, it still conjures up a myriad of horrors, in that builders bum, what's been seen can't be unseen sort of way, and so uncomfortable I imagine
Other than those, crocs, fleeces, pleated skirts in the Barbara Woodhouse mode, can't imagine she ever had a thong on under her sensible attire but you never know! Old lady stuff from yesteryear.
Going to the other extreme, very short tight skirts on women of a certain age. I do remember when I regularly took another child to school with my own when they were very young, dropping him off at his home one afternoon, his nana came tottering out it in skin tight leather trousers and vertiginous heels, immediately opened up a whole new vision of a new age granny, couldn't imagine either of mine adopting such a style even if they'd lived in different times