I (13 at the time) was having a sleepover with my best friend (14), his cousin (15), his other cousin (17) and one of the cousins friend (16). We were at the cousins house. Their mom asked them to walk the dog (it was around 8 at night and it was summer, so it was hot and dark). They live near a small park with a lake. The cousins friend pulls out some firecrackers and we're having fun. One of the cousin's dares my bsf to jump in the lake. And of course, cuz he's dumb and can't say no to a dare, takes his shirt and shorts off, and jumps in the lake. Then we all do the same. I ended up making out with one of the cousin's who, at the time, sorta had a girlfriend (they weren't official but it was basically a thing.) We go back to their place and watch horror movies in the basement. My bsf falls asleep cuddling with the cousin's friend; I fall asleep cuddling with the cousin I made out with.

TL;DR I went swimming with my friends at night, made out with one who had a gf, then we cuddled