Hey man, I did this too when I was in college. Dudes would always leave stuff lying around and most wore hot designer stuff like ck or Polo. One of my hot ass roomates (whos parents were rich) graduated and moved to NYC and left half of his clothes behind. He had nice stuff too! We were about the same size and most of his clothes were nearly brand new. I called asked him what he wanted me to do with it and he said "Dude just take it to Goodwill" I said fuck that, and kept them for myself...including his hot underwear.
Once some of my underwear went missing. It was a pair of Ck Tech briefs with a bright blue waistband and a pair of Tommy boxerbriefs. Whoever took them HAD to have gone though my clothes in the dryer and taken them because I did not leave my stuff lying around in the laundry room, and i realized they were missing when i took them out og thr dryer.
Later one day I saw this HOT dude named Brian who was a out shooting baskets on the court behind the building shirtless and I recognized the blue waistband of my missing Cks. LOL I had seen this dude shirtless before and he always wore just plain Hanes or Jocky Tighty whities. I instantly got TOTALLY hard thinking about him wearing my Briefs and had to jack off.
I later saw him shirtless and recognized the waistband of my Tommy boxerbriefs, so I was 100% sure he was the dude who swiped them. I didn't know if he thought I was hot, and stole the stuff because it was mine, or he just wanted some sexy underwear...but the thought of that HOT stud wearing my underwear sure made me horny!
One day I saw him out shooting baskets again again wearing my Cks and he headed to his apt shirtless so I walked up there and knocked on his door. He came to the door in just his gymshorts and my Cks. I said "nice Calvins man" Where did you get them. He sorta blushed he said umm, umm I bought them. I laughed and said "Dude I know you took those outta my laundry man." He motioned for me to step inside the apartment and closed the door, and said "yeah I did....I am so sorry man" then he started sobbing. He told me that he was gay, and that he sorta had an underwear fetish and admitted that he knew they were mine and stole them because he was attracted to me. I just hugged him and told him It was cool and that I thought he was hott too...and had jacked off thinking about him wearing my underwear.
Needless to say we ended up having sex that afternoon, and became fuck buds after that. Oh, and I let him keep the undies he stole as well as some more pairs he took off of me! LOL