Good question! My weirdest place was inside a paper box in the garage while my mom was looking and calling for me. LoL I was a teenager (13 or 14) back then.
Ofc I also did this in a bathroom of a friends house and even while talking to him (he was outside ofc). I could cum pretty quickly when I was young.
Later in my life I tried to cum in a shopping mall bathroom, but I don't recommend it, because an old pervert noticed the strange movements of my shadows and scared me. The bathroom had a very high space at the bottom but I still thought no one would notice the movements of the shadows.
The old man noticed what I was doing because he was looking for that, he made that gesture with his hand under the opening as someone who wanted to do something or receive my cum. I was really scared thinking he was going to follow me or talk to mall security.
I left there walking quickly and the old man followed me, I had no idea if it was really him, but he was walking right next to me, I looked at him and he kind of looked discreetly at me.
At a fork in the shopping mall corridor I turned abruptly to the right and took another path to another exit, walking quickly so so he wouldn't follow me. I was afraid he was going to say something super embarrassing to me or make some proposal, that would be much worse.
Today I don't do shit like that anymore, jerking off is not as fun as it was.
Reading this is probably difficult, sorry about that. I can only do so much in engrish lol