I had a friend and we would regularly sleepover at each others house. We where in the swimming team together, so we saw each other naked pretty regularly, he had the biggest p***s of everyone.
At home he would always hang around just in underwear, I would follow is lead and hang around in underwear too, even in front of his parents.
One day after I showered at his house, I was dressing in his room, he came in and asked why wouldn't I borrow his underwear instead of using my dirty ones again. I took I'm up on his offer, he gave me a pair of boxer briefs and I left my dirty ones there,