Scared to death!!
The first time I came I had no idea what was happening. I was eleven years old and had heard about cumming from older boys. I liked to look at my college-age brother's magazines he had hidden in our shared bedroom. I would stroke myself while looking at the half-naked women. (This was the mid-1950s and the pictures were tame by today's standards.) It felt so good that I kept stroking for quite a while until something felt very funny. I shot white liquid onto the bed and was afraid it wasn't going to stop. The orgasm was intense. I ran into the bathroom not knowing what to do but grab some toilet paper and hold my cock over the toilet until the feelings subsided.
Once I had figured out what happened I couldn't wait to tell my best friends and try it again and again. Today I am 58 years old, married, and still like to work the big guy two to three times a week. One has to keep the plumbing working or it can get rusty.