I’ve posted about this in a different thread, but if you missed that one....playing sports from middle school through college meant that I spent plenty of time in locker rooms and plenty of time in jockstraps and compression shorts. Since those, especially athletic supporters/cups were required for football and lacrosse we all had them hanging in our lockers. Many of us would rotate what we wore based on daily workouts, or if the previous practice was rainy or really sweaty might wear a backup jock.
Periodically someone would forget their cup, comp shorts or whatever, and would borrow one from someone else. It was an everyday thing, but it was far from unheard of.
I still like swapping or sharing that stuff.