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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
by The Mad shitter May 14, 2003
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An upperdecker is when you poop in the toilet tank of someones bathroom, its the gift that keeps on giving
i was at this party and they tried to kick me out so i gave them an upperdecker
by Nick June 16, 2006
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The upperdecker is a prank that you can pull on a friend or loved one, or more likely someone who deserves it. An upperdecker is defined as defecating in the upper tank of a toilet, allowing it to fester for as long as possible and sending a chilling brown residue into the bowl upon each flush.
At a party where they run out of beer one might like to leave an "upperdecker" to show their disapproval.
by Grant Herman August 31, 2004
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As per the John Waters' film A Dirty Shame, an upper decker is the act of defecating in the tank of the toliet.

(As per my intoxication, an upper decker is my ability to write this while in the act (I'm currently the upper deck).)
"I started doing upper deckers, shitting in the top tank of the toliet, where no one would ever look to find the odor . . . "
by iloverobots01 January 08, 2006
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While at a respected friends house retire to their restroom, stealthily remove the lid from the back tank of their toilet and steady your cheeks directly above it. Begin defecating while trying to keep as quiet as possible. When finished, wipe all remaining fecal spatter from your anus and hide the used toilet paper in the cabinet under said friends bathroom sink. When the toilet is flushed by the next user the bowl will be rinsed with your feces. A firm stool will cause repeated minor fecal rinsing, while viscous, soupy stool will flush out all at once filling the toilet thus causing repeat flushing until clean water is present.
The upper decker was rejoiced by all who were present.
by A Tortured Soul March 04, 2006
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Also referred to as 'Going Up Top,' the act of taking a shit in the tank of a toilet. Common courtesy not to flush. Used TP should be placed inside drawers, magazines, or the tank itself. Feel free to throw in any other items you can find in the bathroom during the process.
"Man this party sucks... I'll let 'em know how I feel with an Upper Decker"

"Dude!! You shit in my toilet" -> "Where else did you want me to go?" -> "Not in the top part you fuck!!"
by ShitBrick February 24, 2004
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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.
by Amanda Huggankiss August 02, 2006
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