My family went on vacation when I was like 18. Our hotel was one room with 2 beds. My parents shared a bed and I had my own bed to myself.

It was late, dark, and they thought i was sleeping. I start hearing a slight creaking, then whispered moaning. The moaning got a little louder and the creaking got a little faster. I got hard. Eventually it stopped.

A few minutes after stopping, I notice my dad gets up to go to the bathroom. I could tell it was him from the dim mirror light when he opened the bathroom door. Maybe 30 seconds later my mom goes in. They're in there forever.

I take this opportunity to jerk off in my underwear thinking about my mom. I imagined my dad pounding my mom's asshole doggystyle against the bathroom sink, then forcing her to her knees and busting in her mouth as she swallowed his load. They eventually come back out and we all go back to bed.

They were early-mid 30s and my mom was super hot back then. Here's an actual pic my dad took of my mom in the hotel in question. Probably not the same night because we stayed there for like 3 days, but you get the picture.