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
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 05, 2006
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!!"
"Dude!! You shit in my toilet" -> "Where else did you want me to go?" -> "Not in the top part you fuck!!"
by ShitBrick February 25, 2004
by afokenr March 26, 2003
the act of sneaking into a bathroom, quietly lifting the lid off of the toilet tank, taking a deuce in the tank and then replacing the lid. this causes the toilet water in the bowl to be polluted after each flush. this is usually done at a party or too someone that you despise.
heath snuck into the frat house bathroom and left an upper decker in the tank, much to the dismay of the alpha betas.
by kirk May 27, 2005
To take a crap in the tank of someone's toilet and not flush afterwards. When the next person flushes your crap comes rushing into the bowl all broken apart. A lot will clog in the top. This is mean.
by Anonymous April 11, 2003
To take a crap in the top section of one's toilet so that when it is flushed, poo water flows back into the bowl.
by King Flump April 11, 2003