Several times.
Once, back when I worked at a manufacturing facility. My parents worked there, too and I was 19 at the time. There wasn't any need for me to drive my car when he all had close to the same shift. I had to wait for them for 2 hours, so I got "certified" and started using their gym facility as I waited. They had two showers in the men's room, however they hadn't any curtain; so once you stepped out of the shower to dry off, everyone walking in would see you.
Initially, it was awkward, then, if I'm honest, a bit exciting, but after a while it became ridiculous. I didn't want people thinking I was a perv for drying off after a shower, so I'd rush it. My manager saw me naked, the gay guy that worked in my mom's department saw me, several maintenance guy and some of the "suits" that didn't work with the products but rather, worked in the offices.
Then, two years back; I was 22 and a friend I sort of grew up with went to the gym. He's a year or two younger than I am, and we'd talk here or there throughout school, but we mostly became friends my senior year. We had the same art class, but once I graduated, we'd just talk here and there about Godzilla on Facebook.
Anyway, we decided one day to hang out. We both found out we go to the same gym. I picked him up one day, we worked out, and then it was time to go to the locker room. I changed clothing, but he went to the gym wearing his workout clothes. Even still, he'd hang out with me in the locker room. A little awkward, but to my mind I was like, "This must be male bonding. Alright." So we'd talk and, after my shower, I tried off, CAREFULLY.. but eventually I knew I'd have to drop the towel and get dressed. Well..
He sat right by me on the edge of the bench as I was standing. Even continuing our conversation, I felt it was getting awkward. I wasn't nervous about my size -- I'm not small and I get compliments on my penis, despite not exactly being 13 inches -- I was just worried about my trim job. I don't shave off my pubes, I just try to maintenance the area. Anyway, I knew he was looking. He just stared at it, brought his eyes back up, we continued talking, he'd stare again, back and forth until I was dressed.. Seemed natural, I guess. He didn't mention it and I didn't, either. We got a bite to eat and drove back to town.