A huge dog that people let get overweight. If it can stand up then nobody will ever break into your house.
Qwerty: "My dad has a friend with a fatty mc fat fat fatty fat dog fat."

Asdf: "Holy shit, can it walk?"

Qwerty: "No, so he has to get carried up the stairs to the house. He's really nice though."
by etaN retsaM March 28, 2008
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Some one who kills you in fortnite/ A freind
*Some one kills you in fortnite* U FAT DOG!!!!!!!!!!!!!!

or
*Yells over to there freind* Hey you fat dog
by Johno1910 October 23, 2018
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to illegally enter someones computer and looking up "really fat dog" on google, downloading it, and pasting it on their desktop as many times as possible as well as also changing the desktop wallpaper to it.
haha dude I really fat doged Jessica yesterday and she was mad with me for days, she had to reinstall her computer because of the lag it caused
by Hitler1337420 February 25, 2019
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A popular saying that you have heard for your entire life.
Don’t sweat it, fat dog it. lay down in the sun and relax, like a fat dog.
by P1x13f1sh November 29, 2022
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