babooning
When you and your partner sit on each other’s butts and you both start jacking off through your pants like it's a competition.
My friend and I went ass-to-ass and jacked each other off like it was a competition.
At the park, I went ass-to-ass with my buddy and we both jacked off.
During lunch, my sister and I went ass-to-ass and we both jacked off like maniacs.