Upper-decker 

using the water retaining bowl of the toilet, instead of the toilet itself.

that beyotch pissed me off, so I ate 3 large burritos, took some Ex Lax, went over to her house and left her an upper-decker to deal with.

Upper-decker by Amanda Huggankiss August 2, 2006

upper-decker 

the act of taking a shit in the cistern of a pub or restaurent toilet to highlight dissatisfaction at service or food standards.

causes the water flushed into the toilet to be shitty. and lets face it, who is gonna take a turd out of a cistern??? muuhahahaha

upper-decker by UnCLe_MeLLoN_BaLLs April 7, 2003

Upper Decker

Step 1) Make sure nobody's around.

Step 2) Quietly open the lid of the upper-section of the victim's toilet.

Step 3) Quietly place the lid down on the floor.

Step 4) Then take a nice shit in the upper-section of the toilet without letting anybody hear you.

Step 5) Wipe your ass.

Step 6) Place the soiled toilet paper in the upper-section of the toilet or in a drawer or magazine.

Step 7) Slowly lift the lid off the floor with your fingers under it and carefully bring it over to the toilet.

Step 8) Here's the hard part; with your fingers under the lid
slowly place the lid on the toilet. No false moves or you're screwed.

Step 9) Leave and don't let anybody see you. Just bail as quickly as possible.

Step 10) Mission accomplished.

Plumber: It looks like you have feces in your toilet's tank.

Victim: It must have been an upper decker.

Plumber: Yeah right. Its already clear that you're stupid enough to shit in there!

Upper Decker by Mike_Litoris June 29, 2011

Upper Decker

The act of taking a dump in the tank of a toilet.
Step 1: Quietly sneak into the bathroom unseen
Step 2: Carefully remove the top of the tank. Note the porcelain tank top is very delicate and will shatter if dropped

Step 3: Climb on the toilet, drop pants and sit on the tank. Imagine you are a bird sat uptop your nest, sit very softly or else the tank may break and the operation will be compromised

Step 4: Take a monster shit. I'm talkin like a goddamn mudslide out your asshole

Step 5: Whipe and throw the tp in the tank too for good measure and put the top back on

Step 6: Return to the party and act like nothing ever happened, if you leave right away you will draw suspicion to yourself
Step 7: Enjoy the host's reaction when they see that Mount Vesuvius just exploded in their toilet tank

Friend: Yo did you hear, Julia is having a party this Saturday
Me: I dislike her very much, I'm gonna drop an Upper Decker at that party

Upper Decker by bowelsmovin June 25, 2017

upper decker

The act of defecating in the upper tank of the toilet. When the next poor unsuspecting person flushes the toilet they get a bowl of beef stew. the upper decker is a weapon of terror and should only be used on people who deserve it.

My friends x-girl friend had a party and she left whith some other dude who looked like the fonz "Heyyy!". So I took it upon myself to leave her an upper decker

upper decker by The Mad shitter May 14, 2003

Upper Decker

The act of taking off the back lid of a standard toilet, hovering your anus over the opening and shooting diarrhea into the tank water. You must then wipe with TP and leave the TP in the tank. Adding red food dye to the tank is called BUD, or Bloody Upper Decker. Either with or without the dye, when the next person who uses the toilet flushes, the water that refills the bowl will be the most vile, horrific, stinky fluid known to man. Woman have been known to scream and run out of the toilet as they think their insides are coming out. Key stuff here.

"I was working a night party at that rich cunt's house. As the party was ending, I asked the beeotch if I could make a sandwich. She yelled at me in front of her guests that I will "eat with the rest of the hired staff at the end of the night!" A simple no would have been fine. For a thank you gift, I pumped a gallon of milk into my lactose intolerant ass and dropped and Upper Decker that cunt's main bathroom. Later, I Bloody Upper Decked (BUD) the upstairs daughter's fine china toilet. After that I raw dogged one of the workers and bailed, yo.'

Upper Decker by Dick Smartly July 3, 2014

Upper Decker

The act of shitting into the tank (or upper portion) of a toilet. Done as a prank, it results in at least four foul flushes (also known as a "3-F qualifier") afterwards.

"Man, I'm gonna fucking puke."

"Dude, how come?"

"Man, someone dropped an upper decker in the toilet, and the water splashed my ass and sack."

"Dude, that sucks."

"Man, I think I got a piece of corn stuck to my sack!"

Upper Decker by papamikedelta October 24, 2009