[verb]ing the [noun]. Seriously, it's masturbation, use the right inflection and anything is a euphemism for it.
Jilling off (as in, the opposite of Jacking off). My old job had a calendar we would use for requesting off. Whenever my supervisor Jill would write "Jill Off" on the days she needed, I would always say "I guess we know what she's doing that day." Everybody at work thought I was really funny and liked being friends with me.
Raping your mother Beating your children Injecting your botox Hosing your housewife Posting on your porn thread Ballsacking your hairbrush yeah, not gonna work..... (Interestingly, in trying to continue to disprove Aetius's post, I came up with a few more appropriate ones Beating your pitbull Punching the homeless man/woman Going postal on your pussy Stuffing your mailbox Ringing your doorbell Rafting the river Answering the other line Fumbling the football (yes, came up with this while watching the Dolphins' shitty special teams)
I am partial to "Deejaying". As in "Sorry ladies, can't go out tonight. I'll be too busy DJ-ing [my clit]." Because, honestly, it's the same hand movements and everything. But I've also heard: -Labia Lovin' -Fingerbanging -Giving yourself a Wet Wendy -Spending alone time with yourself -Pussy Playtime
Gutting the fish. (I like to use this one as a sex euphemism but it also works for masturbation, in a weird, surreal way.)
Shaking the dust off the drapes. Washing the beef curtains. Denying the masses. Alice going down the rabbit hole. Slippery dipping. Five finger discounting. Canoeing down river. Filleting the fish. Tackling the taco. Spelunkering. Teaching kitty to do tricks.
Sexually stimulating oneself by the stroking of the clitoral area and/or internal penetration using one's fingers/ assorted sexual toys or any combination thereof, usually to the point of orgasm.