Part of the joy of talking about sex is how we use euphemisms and idioms and other creative ways to communicate one of those “not in front of the children” actions.
Looking at The Big Book of Talking Dirty, I was amazed at how many phrases people have used to refer to the Biblical Onan's sin (actually, it wasn't masturbation; he prematurely ejaculated, but that's another story).
Here's a few interesting sayings that might “tickle your fancy” (which doesn't mean masturbation; it wasn't on the nearly 20-page list in the book):
“converse with Harry Palm” (1990s); according to the book, perhaps a reference to the hairs that grow on the masturbator's palm; it could also be a reference to Len Deighton's anonymous intelligence agent, named Harry Palmer for the films (1960s) starring Michael Caine
“to make a foreskin cone” (1990s); all I can say is, yummy!
“drain Charles Dickens” (1990s); how literary.
“to have a conversation with the One-Eyed Trouser Snake”(1960s+); try and visualize that one. Scary.
“free willy” (1990s); yep, it's from the movie about the killer whale.
“box the Jesuit and get cockroaches” (late 1600s-early 1900s); you know, those evil Catholics spreading all kind of perversity and disease…
and, last but not least,
“to know yourself” (late twentieth century).
In this case, ignorance is not bliss.