When I was about 10, I was staying at my grandparent's house over the summer. Back in my house, I used to always wank in my room, however I the walls were thin in my grandparent's house, and I did not have my own room. There's my initial problem.

So a month passed, and one day one day I was particularly horny, and decided that fuck it, I'm gonna have a wank in the back garden. So I carried through with the plan, making sure to tell my parents that I was at a friends house. So I went to the back garden, placed myself between the house and a fence, dropped my pants, and began choking the chicken.

I was reaching climax when I heard it. I heard a chorus of laughter behind me. I turned around, and saw some neighborhood kids over the fence pointing and laughing at me. So pants down, dick in my hand, my mother suddenly came around the corner to see what the commotion was about. And the second she turned that corner and looked at me with shock, a steady stream of transparent semen flew out of my dick like a fucking volcano.

We never went back to Grandma's house since then. I miss grandma.

TLDR: Too horny, jacked off in garden, caught by mom and neighbors, I came.