When you take a crap in the tank of someones toilet instead of the bowl. Most often done to a sworn enemy or to your best friend.
by Helvis September 16, 2003
When someone poops in the top part of a toilet, (the part that you have to take the top off) so when someone else goes to the bathroom and flushes the toilet instead of clean water coming in and filling the toilet, shit water comes in. This is done as a pratical joke, usually done at parties.
Guy 1:Hey I just did that Upper Decker in the toilet upstairs and Jennifer went in there.
Guy 2:Hahahah, what'd she do when she came out?
Guy 1:I don't know, she's still in there!
Guy 2:Hahahah, what'd she do when she came out?
Guy 1:I don't know, she's still in there!
by Kevinnnnnnnnnn December 26, 2009
by Goldgoatturd February 20, 2009
(Film Critique). When a movie starts out engaging and has great potential, but then the ending falls apart and the whole thing turns to shit. It's like finding an Upper Decker when you flush your toilet at the end of a party. It's there, and it's shit, you just don't know it yet.
by Britley's Grams February 22, 2016
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 :)
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
Bro: Are you serious? Thats messed up. You really know about upper deckers
by t-bozz January 29, 2013
by DaddyFatSizzles March 29, 2011
the act of deficating in the upper tank of ones toilet leaving a foul stench undiscovered with the remnants of muddy water
by face vol.4 May 24, 2009