Once, I was shopping in Walmart and saw a beautiful woman who was hardly dressed. Obvious nipples and camel toe on full display. I was immediately hard and horny as I saw her. I began discretely stroking myself through the pockets of my shorts following her through a few aisles. I seriously doubt she did it for my benefit but she began looking thought the bras and panties while I stopped in the men's section to watch as she held up some very skimpy, sexy panties. It didn't take long before I shot a good load into my shorts. With a pretty good size wet spot on my shorts, I walked past her smiling at each other as I left the store.
Once, in class during 'study hour'... a very slow build by pulling back on the skin just under my head, holding it and repeating until I came. I remained silent, but my breathing was probably noticeably labored as I came in my boxers.
Later in life, on a hike thru the dunes, I found a somewhat secluded trough, laid down on my side to minimize the view if someone came over the hill behind me... in full summer sun, in nothing other than a bathing suit, I shot a handful of ropes of cum onto the hot sand.
Pulled over on the road got out and went behind a tree and let it go. I travelled for work and did this several times, same tree. I'd sure a few people who drove by and saw a guy in a suit and tie behind a tree.