This happened in the 80's when shorts were well, short. I used to go to the YMCA in San Francisco during lunch with a coworker. He was obsessed with my dick and I would tease him all the time just to get a reaction from him. After going to the gym for several months, I decided that I should get some cardio instead of just lifting weights. So I decided to run right along the waterfront on the Embarcadero. It is a pretty wide sidewalk with other joggers and blade skaters. I have to say, I am not really a runner. Never really liked it even when I had to run every day in high school when I was on the wrestling team. But I thought the cardio would be good for me.
I wore my white gym shorts like I normally worked out in, no jock strap, no briefs, just me and my dick. As I started to jog, my dick was flopping around all over the place in these white shorts. It looked ridiculous, but I figured if my dick didn't show, then I couldn't get in trouble. The problem is, I started to get a semi with all that flopping around. All the sudden about 3 inches of my dick fell out the bottom of my shorts. Now, freed from my shorts, my dick was swinging around like crazy until at least half of my dick was showing. The longer it flopped around, the more would be exposed. As thrilling as that was, I knew I should shove it back in, which I did. But it was right out in public with a lot of people that definitely noticed. We kept running and my dick kept dropping out the bottom of my shorts every couple of minutes. My friend went nuts seeing my dick flopping around and falling out every few minutes. You can imagine how horned up I was. We made it to Pier 39 and I decided to look for a restroom. When we got there, I pulled out my still semi-hard dick and just started jerking off while my coworker watched. He had a little dick and was always embarrassed to show it. But he didn't have any problem encouraging me to show my dick off to him every chance he got.