well,I went to a boarding school, lived in a dorm. Had a guy open the stall door on me right when I was cumming, he closed it real fast, I don't know what he saw, he never said anything, ............had my roommate come in right when I had finished cumming, still had the Playboy out , actually still had my dick out, I tried to hide it all but he knew, he stifled a grin, looked off into the distance as he talked to me and never mentioned it.
Was doing it on the back porch of my apartment once, a girl coming to look at a vacant apartment turned the corner and said "Hi" when she saw a person but didn't yet recognize what they were doing, I said "Shit" and jumped out of the chair and through the door.
Those were the most flagrant, I've been caught other times but was able to hide it because I was under the covers or what not, and my parents "caught" me by finding my stash of bikini and lingerie pages from department store catalogs. I was coerced into giving them up to my mom. I was coerced into saying I would refrain from doing it, but as I uttered those words I had NO INTENTION of refraining.