A girl or guy you keep around to make yourself appear more attractive. They usually have some outstanding quality like humor that makes them worth having around.
Bertha is funny,sweet and smart but she is my fat friend so everytime we hit up the club i get all the guys and the attention.
by nina Campbell October 12, 2007
The obese/chubby friend of a hot male or female that can always miraculously keep them out of a relationship with you. The best thing to do with them is to friend them, then start a relationship up with your target. Afterward, do something that will cause the fat friend to split up with your lover, so that there will be no more of her/him.
Dave: My god man, that woman is soo hot. The things I'd do to her...
Jason: Good luck, man. Her fat friend always pulls her outta here before you can do anything.
by AdolescentWit June 22, 2009
The best way to refer to your wife's friends.
I could have gone to the Super Bowl if it weren't for you and your fat friends.
by WackyJoe February 9, 2010
A grossly overweight and bitter young woman who finds a social outlet by becoming “Best Friends” with a much more attractive girl then manipulating and ultimately controlling her life to live through her.

Extremely hostile to most of her attractive friend’s friends and especially all of her boyfriends. Will interfere constantly with the view to splitting them up by any means necessary.

Will constantly “Feed” her victim until she’s approaching the same weight category and level of unattractiveness.
Dave: "She was alright, that bird. You slipped up there, Jim."

Jim: "Wan't my fault, Dave. It was her fat friend sticking her oar in."
by UpYourKilt August 28, 2011
the theory that states all hot chicks have a fat friend. also see wingman
the fat friend theory is almost always true.
by jmobley October 5, 2006
The fat, ugly girl who hangs out with a group of very attractive women. The big fat friend is a notorious cock block and will do whatevr she can to prevent you from sleeping with her friends. Her biggest weakness is the non-discriminating wingman who will sleep with anyone.
I was macking on this girl, but her big fat friend wouldn't leave us alone.
by Mufasa25 October 2, 2008
Usually a female friend of your girlfriend. You HAVE to get on with her for the sake of your relationship but she doesn't make it easy! She'll make sarcy comments, Make fun of you and demand to be everywhere that you and your girlfriend go.

Listen to "Big Fat Friend by Stephen Lynch" for more info :P
Guy 1: Oh hey did you end up getting with Rachel last night?

Guy 2: Nah her Big Fat Friend was there the whole night, Wouldn't fucking leave man

Guy 1: That sucks, just bring her a picnic basket next time!
by Killleera7x December 23, 2008