The first time I can remember cumming in public was my own backyard. I lived at home with my Mom, in a normal suburban house with a front and back yard, but small. The back yard had a deck attached to the side of the house where we had some patio furniture, and the yard was large and open with no trees. The deck was raised up slightly above and looking over the rest of the yard, I would often see our neighbors through the low chain link fence on both sides doing yardwork, and turning their lights on and off as the day went by.
One summer, my mom decided to rent a hot tub for a week. It went right on the deck next to the house, and we had it for a whole week. I didn't think much of it for the first few days... My mom had rented it for a party she was having over the weekend. The party went off as normal, a dozen or so of my moms middle aged friends drinking in the house and yard - gave me lots of time to smoke weed with friends and do my own thing.
After the weekend passed, my mom let me know we still had it until Friday. I hopped in once or twice to relax in the middle of the day. It was nice, but everything changed for me one night when I decided to go down to the hot tub after my mom went to sleep. I cant remember if I was thinking about jerking off in the hot tub when I was heading downstairs, stripping to nothing but my bathing suit, grabbing a towel. I remember making sure my moms bedroom light was off, confirming that she wouldn't be up for the night.