Would anyone with a modicum of common sense look at a ladies thong and think "Ooh yes, great disguise! No-one will ever recognise me while I rob that shop if I've got a thong on my head!"
In Colorado, two men used skimpy women's underwear to disguise their faces while robbing a shop. One wore a green thong pulled over his face, and one wore a blue one, while they stuffed their stolen items into a pink rucksack. They turned themselves in after being caught on CCTV. If you were intent on pursuing some dodgy activity and wanted to hide your face, I can understand you would get a bit more coverage from a hoodie or a balaclava as there's obviously more fabric in them, but thongs???