I wound up--never mind how--on the Wikipedia page that has slang terms for masturbation. It's awesome. I recommend that everyone go and look at it right now. For anyone too lazy to click the link, here are some that I really love:
white water wristing
stroking Gandalf's beard
having a mastie
punching the munchkin
double-clicking the mouse
chafing the yard
killing Tony Danza
jostling the elder
strumming the one-string banjo
writing in your journal
and my favorite: having a conversation with James Lipton
It's true that you can make almost anything sound like a euphemism for jacking it, but I think that these are especially creative. And I have absolutely no idea how "killing Tony Danza" applies to the topic, but goddamn, I love it.
