When I was in 10th grade, my male classmates used to "fist" each other. They repeatedly bumped their fists against each other really fast (bro-fist or how it's called) and made moaning noises. The popular boys did this, the ones that were the quickest to call someone gay as an insult and who rather got an F in P.E. than touching another guy during Judo lessons. At first I thought it was meant as a joke or to mock gays or something, but they seemed to take it strangely seriously and didn't even laugh about it. I think they had to release sexual frustration because no girls wanted to bang them. I don't wonder why.