A Faux Decker is executed by:
1) Opening the rear tank of a toilet and dropping in a piece of novelty rubber dog poop;
2) Pouring in 1/2 cup (120mL) of instant iced tea mix into the tank as well;
3) Replace the lid and leave the Faux Decker for the next unsuspecting victim.
Upon flushing the toilet, a brown stew will be unleashed, horrifying the user and leading them to open the rear tank...only to see the fake poop and surmise they have been struck with an Upper Decker.
The Faux Decker is a more sanitary prank than the insidious Upper Decker, but you get almost the same shock-value from the Faux Decker as you would the original.
Dude 2: "Why a Faux Decker not an original Upper Decker?"
Dude 1: "DUDE, she's my Mom! I wanted to freak her out, not make her disown me!!"