look up any word, like the eiffel tower:
 
1.
An offensively large dump. A crap of such grave proportions, that should the cruel bastard decide to deliver it whole (without any effort of pinching it off, flushing in between), such a deed would amount to nothing less than an act of pure, unabated vandalism; a destruction of public or private property, with due compensation and mandatory letter of apology to the caretaker of said toilet.
Accomplice: Where ya goin?
Offender: Just poppin' into the loo to squeeze out a fat rat.
*closes door*
*speaking through the door, the conversation continues*
Accomplice: Have you prepared you're letter of apology?
Offender: Aye, writing it on the walls as we speak.

"The fuck?! Who broke my toilet? Whoever just laid this brick, fess up now, or when I find out, I swear I'll shove this fat rat back up your cursed cornhole so far, you'll be belching farts for the next week and a half!"
by TSVandenberg July 11, 2012
 
2.
A Guinea Pig... A vile little creature that resembles nothing so much as a rat, if that rat were designed by GM and built by AMC.
Mom: So... Would you like to get a pet?

Kid: Sure. Anything but a fat rat.



A: What -is- that smell?

B: Oh, that's my brother's fat-rats. He changes their litter about as often as he showers.
by Honor July 22, 2008
 
3.
fartso marsters
Y'alrite fatrat
by Pete Willis June 04, 2003
 
4.
An overweight woman.
Geez, are all Tri Delts fat rats?
by LordWatson July 12, 2003