When my BF (now DH) was staying with me for 6 months one year - we lived in different countries and it was his chance to get to know my home country and culture - a friend of his visited us.
First, we spent a few days with my parents, and while he was a bit awkward, there was nothing special to report. He's always a little awkward socially but a great friend and my parents saw through the awkwardness and liked him a lot.
Then the time came for us three to head off to my little student appartment. It was just after Christmas and I'd been home a few weeks, which meant there was no food in the appartment. Mom gave us leftovers to take with us - both guys were right there, watching and even picking things they'd especially liked.
A 3-hour-drive later, we got to my Uni town, we did some sight seeing and everything was dandy.
We got home, I warmed up the leftovers, thinking I'd probably taken too much, as we were going out for dinner the day after but decided I could freeze the rest for myself.
False alarm. I went to bed hungry that night. Before I could even really get to the table - I did tell them to start while I was still heating up things - almost everything was gone and my BF had hardly eaten a thing either.
Friend ate four plates of turkey stirfry and two plates of carrot-rice casserole.
That evening, as we were staying in my tiny student appartment, I was the first to disappear into the bathroom with my pajamas, get ready and changed. My BF was the next. I believe he even said something in the tune of: "Ok, off I go to change, I guess you don't care to see my hairy butt, Friend" as he gathered up his stuff. While BF was in the bathroom, Friend and I were talking, both relaxing on our beds (well, his "bed" was an air matress). All of a sudden, he took off his sweater and folds it neatly. I thought nothing of it.
He then took off his jeans and folded them neatly.
And his t-shirt.
By that time I was starting to get a little frazzled.
When he took off his boxershorts while lying down, I was too shocked to say a thing. I just looked the other way and hoped it'd be over soon.
He kept chatting and when my BF got back into the room he was in his pajamas.
I told my BF what had happened and he had a private talk with Friend and made sure he'd only change in the bathroom from then on.
ETA: wow, thanks rashea for letting me know