A Dumpster Baby is when you lift the lining out of a garbage. Preferably in the bathroom, then take a dump in the can. Now, put the lining back in and let that bad boy marinate. When the dumpee lifts the lining out, he will have a nice drippy mess of a dumpster baby.
"Dude, I just took an amazing dumpster baby in my buddy Jeff's bathroom. It was epic."