It's when you're fucking a girl with a condom on, and you're so drunk that you don't know if you're going to piss, or cum. You pull out, roll the condom down to the tip of your dick, and fill it with whatever fluid comes out. Then you take the condom, and slap the bitch accross the face with it. Right as it whips accross her face, when it is far to late for her to evade the swinging specimen, you yell "DUCK!"
"Dude, I'm so wasted, but this girl want's to hook up with me"
"So, she's hot, fuck her"
"I'm too drunk man"
"Just do the rubber ducky, she looks like a VD slut anyhow"
A rubber sheet is a protective covering to keep your bedding dry.
When I was a teenager, my Mom put a rubber sheet on my Wonder-bed because that's where I jacked off every morning and every night - and I really blow a load when I cum!
"I'm having an affair with my next door neighbor's boyfriend, only she's a great friend and I don't know how to tell her that I'm in love with him. It's all just so rubber-biscuit."