Laying in bed, chubbed up, waiting for your roommate to go to sleep so you can pleasure yourself
"I had a Louisville Slugger-sized hardon last night and needed to crank one out, but my roomie was awake, watching some dumbass videos. I was up masturwaiting until 1:30am!"
Waiting for everyone in your house to go to sleep to spare having to hear them or them hear you while masturbating.
John: Why the hell are you so tired?
Bill: My brother wouldn't go to sleep, I was masturwaiting until like 2AM for fucks sake.
John: What the fuck is masturwaiting?
Bill: Check urban dictionaryfag.