It seems to me that there are a lot of funny phrases for male masturbation and not many for female, Rubbing one out comes to mind. But for men, there are many. I would like to see if there are any I have never heard, so I will start: beating your meat; bopp'in your bologna; flogging the dolphin; boxing the clown; rough'in up the suspect; Feel free to add
Back in the 1950s, "pulling yourself off" was the main one at boarding school. I still use that as I watch porn and masturbate.