Oh god
Well, when I was younger (around 3/4) I used to get into bed with my parents some nights but before I would join them, I'd press my ear against the wall to see if they weren't doing it. One night, I didn't hear them so went to join them. I opened the door and all I could see was my Mum's leg raised in the air and my dad going at it

I've never seen two people react so quickly in my life, my mum shouted "GET OUT!!" at me and I ran back to my room so fast. I didn't sleep in their bed for like 2 months.