I used to do this from time to time with my best friend in highschool. We played soccer and were gymnasts together, so had seen each other naked lots of times.

Once, I stumbled back to his house with him after a party. It seemed as if each of us had been drunk, high, horny, sexed up and covered with sweat and semen at some time that night. We each took a shower, and went to sleep naked (he had twin beds) in his room. In the morning, when we were more or less awake, and more or less sober, I borrowed a pair of his briefs and a t-shirt, and walked to my own house after breakfast.

His mom was kind enough not to say anything (I mean, after all, we WERE all of 16 years old!) about how we looked, or our lack of ability to concentrate.

I washed his Jockeys and t-shirt, and folded and returned them to him. I borrowed underwear from him later on as well, and he borrowed from me. He was hung pretty long like me, but not as thick, so it didn't feel all that weird wearing his underwear.