Regular sleepovers at my best friend's in middle and high school. My dad took a college teaching job on the opposite coast when I was a senior, and his parents "adopted" me for the year. I stayed in his room, which had twin beds. Neither of us wore any sort of pajamas, and both of us woke with regular morning hardons. We'd often share his bed, in a non-sexual way.
My college roommate was totally oblivious to me being in the room when he'd fuck his girl friend du jour. Many's the time they'd come in after I was asleep, screw a few times before they went to sleep. Then they'd fuck again in the morning, and Robbie would climb out of her, his cock still hard, to discard the condom in the trash, before he'd head to the shower room down the hall.