I dont know if this qualifies as accidental, but I can guarentee I wasn't supposed to see. I was visiting my grandparents, when my friend, his older brother, and his brothers gf came over with their family. She was around 17 or 18, and me and my friend were 12 or 13 at the time. It was dark out and we were outside fucking around when we decided to try and find them or spy on them. Just kid stuff, we eventually found them. They were in my grandparents basement, which only has to windows. The one on the door to the basement and a small 1 foot by 1 foot by the ceiling. Luckily it was right below their deck and the yard sloped up to it so you could see through it without anyone knowing you are there. So we watched them make out for time, probably laughing our asses and being dumb. After a few minutes his brother pulled her top off. Holy. Fucking. Shit. I should have stated earlier that his gf is fucking hot. A complete 10/10. He always dated dimes. Her boobs were amazing, they were pretty big, perfect nipples. It was awesome, she ended up blowing him so we walked away cause it was getting weird. The next day I went out on their boat with them, and she was of course in a bikini that thankfully didn't cover much. I learned that day when out on a boat with a girl in a bikini, hit as many waves as possible.