I am 19 (was 18 a the time of this). 5’10”, 150lbs, 4.5″ and cut (yes I am very much on the smaller side).
This happened just over a year ago. I go to a gym that has a sauna attached to the locker / shower area. I’ve sat in there a couple times before. On this day in particular, the gym was very empty (around 20% of normal). The sauna room just had 1 other guy in it. He was an older guy (in his 50s?), more fit than I am, but not super muscular.
I go in there. He is sitting against the back wall. I sit on the side wall. It isn’t that big of a room, so by default I wasn’t that far from him. 2-3 people could sit in between us. I have nothing on but a towel around my waist (as normal in there). He makes eye contact as I enter, but nothing more than what one would think is just an acknowledgment of my presence. I sit down, close my eyes, and tune out. 5-10 min later, I open my eyes. He is still sitting there as before, but has a massive tent under his towel. It looked huge, and I couldn’t tell if that was really just from his cock being hard. My eyes became fixated on that. A few moments later, he realized that I was staring. I was still staring at his massive bulge, and didn’t really think of the fact that he was watching me stare at him.