I used to frequent the gay baths, where guys are expected to wear only a Towel in the cruising areas.
On my very first visit to the baths at age 18, I opted to keep my underwear on under my towel. After walking around for a bit, I got picked up by a guy aged around 40+ who took me to a private room, sat down on the mattress, opened and removed his towel, and said he wanted to suck me off.
He took my towel off (and I draped it over my shoulder), pulled down my undershorts, and started sucking me. Note here: I was very shy as a teenager and rarely even took my shirt off. Prior to that first visit to the baths nobody had seen my dick since I was a boy. It felt weird standing there with my jocks around my knees being sucked off by this older men.
On later visits to the baths I ditched the practice of wearing my underwear under my towel.