Hi Artful,
I did something similar and loved it so much but had to stop. When I worked downtown Chicago there where an abundance of gyms in walking distance after work hours to hit up to work out yes but I had other motives. I would scope out the gym hard while working out seeing what guys I found to be most attractive and keep those mental notes. I made sure to get on a piece of equipment close to the men's locker room door and as soon as I noticed one of those men enter I followed in shortly after. Using what possible reason (depending upon the lower room set up) to pass by the guys locker (bathroom/whatever) making another mental note of what locker they where at. I would go to my own locker area or the bathroom and want to hear this bud get into the shower. I quickly ventured back to their locker, which unusually always seemed open or unlocked still grab those undies and sneak off into the bathroom stall with them. I would inhale all those yummies and allot of times just cum all over them. Cleaning off the rest of the cum my cock and balls with said undies to further defile them. If the bud was still in the shower at this point I would hightail it back to their area and put them back with my seed all over them. If the bud had already return to their locker I would just hid them in my locker and use as a cum rag and sniffer a little while longer before getting rid of them. Hell if they were really nice I would wash and than keep them but hardly did that.
That really took me back and make me horny as well. I think I almost had precum writing this. I had to stop because it was becoming a bit consuming for me and the front desk people began raising some eyebrows along with some of those cute guys whose undies I defiled.
Hey, it's not like those times at the gym when I would walk in completely naked into the sauna with stroking my hard dick asking the other men if they were gay and wanted to play. I took the more subtle approach with the undies.
Geez I am horny again, going to stop now and thank you for that release. I need a cigarette now and I don't smoke anymore.
Hugs, tugs and rubs