Lol. It was your birthday, but really for one of them it was THEIR birthday. Maybe more guys are into it than we thought... Or it's not something they think about until it just hits them. Like maybe one of them used the bathroom and saw it and just in the moment was curious. He obviously liked it enough to keep them. I would have left them there, but definitely sniffed them. Just one pair of underwear on the floor is too obvious that they'd notice. But it was a party of guys like you say so I guess you'd have no clue. hahaha
I didn't even think about it but there were girls there too. I hope none of them took it and it was indeed a guy. Would love to know which one of them took it though, maybe il see them wearing my boxers one day and confront them about it ha.
























