look up any word, like fluffer:
 
8.
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.
It was my last day of work, and a friday to boot...so I left an upper-decker in the men's room.
by Anonymous April 10, 2003
 
9.
A vengeful act of defacating in the tank of a toilet so as to odorize the bathroom with every flush for weeks until found. This is usually done at parties where you don't like the host/hostess.
"everytime I flush the toilet my bathroom wreaks, someone must have left an upperdecker, when I said the parties over go home..OH man! they did."
by troy garner September 02, 2005
 
10.
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
 
11.
A toilet prank, whereby someone defecates in the refill tank (water closet), causing each additional flush to deliver brown, poopy water into the bowl.
Jim was being such a jerk at his party, so I went upstairs to his bathroom and dropped an upper decker in his toilet.
by bodythunder November 12, 2008
 
12.
The act of removing the lid off the back part of a toilet and pooping in it. Poop comes in the bowl over time after flushes. Usually done at big parties that have gone wrong.
The host of that party was so horrible that Andre couldn't resist pulling an upper decker before we left.
by Agenda July 12, 2005
 
13.
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
 
14.
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 26, 2005