36
The act of defecating inside the water tank of a toilet.

Step 1: Go to the home of your mortal enemy. Ask to use the bathroom.

Step 2: Approach toilet and remove the water tank lid.

Step 3: Step on the sides of the toilet and squat over the water. Carefully take a massive dump. Wipe your ass and dispose of toilet paper in the trash bin.

Step 4: Place water tank lid back on the toilet.

Step 5: Escape.

What happens? With each resulting flush, it will fill the bowl with a chunky brown water. Its the gift that keeps on giving :)
Lady mere mere: Just took a massive upper decker

Bro: Are you serious? Thats messed up. You really know about upper deckers
by t-bozz January 28, 2013
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37
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
by bowelsmovin June 25, 2017
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38
AN ACT OF WAR. To take shit shit (some crazy how) in the upper tank of a conventional toilet. The next flush will be your shit and shit colored water. WARNING: The tank will be saturated with your shit. Hence the WAR about to commence. Do not do this without an immediate exit plan. And a fucking follow up plan of how and why you did such a fucking nasty thing.
I took and Upper Decker and dipped. Because I hate that fuck. And I am also a nasty unhygienic piece of shit whom wanted to fowl their party and embarrass.... fucking however.
by theutopianing April 18, 2012
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39
To put toilet paper over someone elses poo when the toilet is clogged and then take a shit on top of the original poo.
I shit on eric's poo because he clogged the toilet and there was nowhere else to go.
by grind January 16, 2004
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40
The Act of taking a shit in the Upper Tank of the toilet as a prank.
by DaddyFatSizzles March 29, 2011
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41
to leave a nice steaming terd on the toilet seat, enhancing the savory odor for the next user of the john; especially irritating to females, dudes not so much. Not to be confused with a Back Door Bandit which involves removing the lid of the reservoir tank and much better balance
eww, gross!!! some fuckwad left a upper decker in there!!!!! take me somewhere to tinkle, dammit!!
by coldbowl May 17, 2007
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42
When you take a dump in a toilets tank
Dude: im going to take an upper decker in burger kings toilet.

(Dude upper decks BK)
Later someone takes a piss and flushes toilet: what the!
by mountain high mush September 13, 2014
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