This one comes from my wife's wild younger days. She had gone to a house party with her boyfriend, and after a while of drinking and partying she'd gotten pretty drunk. Her boyfriend took her into a bedroom to fuck.

She remembers that they fucked doggy style, with no condom (she was not on birth control) and he ended up cumming inside her. She remembers that at this point her boyfriend left, but she just stayed in the room naked, full of cum.

After a little while (she says she was so drunk she has no idea how long), a friend of her boyfriend came in the room. He then fucked her too, again from behind, and came inside her.

She found out afterwards he'd checked with her boyfriend if it was ok, and it was, though at the time she wasn't in a mental state to check and be sure, she just went with the flow and took his cock. She's told me she loved knowing that he was fucking her while she was still full of cum, and that he was allowed to use her.

Nothing quite like it ever happened again, but it's definitely fueled her kinks in a lot of ways regarding freeuse and hotwifing.