School bus sex

I was a freshman in highschool when this happened. I just left school ready to hit the road on the bus. Only a few kids got on the bus, 2 juniors and 3 freshmen. Even on the first day of highschool I established my seat. very back seats far right. noone else sat back there often so I had the back all to myself. Anyway, apparently the female junior fell asleep and 1 of the freshmen got of at her stop. So the remaining people were making "akward" coversation about porn and things surronding that subject. I just backed out of the conversation. The other junior(male) was accompanied by the other freshman(female).(they sat next to each other). The freshman sat on his lap and they talked casually, bringing me in once in a while, but i wanted to mind my buissness. so as few a couple of minutes, while i was enjoying the outside of my window, the freshman's position changed. She was now sit on his lap virtically, facing away from him. I thought nothing of it cuz people did that all the time at my school. But the thing that got me interested in what they were doing was the constant up and down motions the freshman was making. They were small up and down movements but you could see she was moving up and down. it wasn't untill i saw a little side boob when i realised they were having sex. even though they didnt make noise, it was obvious to me. They were good at keeping the noise level down. At first I was like "wow seriously on a bus c'mon" but after a while it started to get a little erotic. they made a little sound but that was enough for me to start stoking my cock slowly but i had to be mindful of the sleeping junior(female btw) who could wake up at any minute. The freshman's stop came and she got her things and left but i saw a bit of her underwear hanging from her pants. All i could give to the lucky Junior was a thumbs up. So what do you think about this?