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1.
(noun)
A person most widely known for the fat that forms mainly around their ass as a result of the ingestion of McDonalds

While found in other countries, the McFatAss tends to breed most successfully in America. They are most comfortable in packs of 3 or 4. However, their shitty 1991 Honda Civics don't usually allow the easy transportation of these packs. Their natural enemy is the scale, stair-masters, gyms, P.E. teachers, movie theatre seats, airline seats, single servings, and anything healthy.

In their natural habit, (a McDonalds of course)they can be very easy going and possibly friendly.
DON'T BE FOOLED! For as soon as the McFatAss is out of its comfort zone, it will attack! The most common form of attack has been biting!

The McFatAss is usually not born fat. It usually develops a sweet tooth for fast food later in life. However, if two McFatAss mates (usually unsuccsessful because one of the two will either have a heart attack, or be crushed to death by the other)they will create a McFatAss baby! The McFatAss baby is very cute when first born. However, that cuteness will soon turn into an ugly McFatAss.

There were a few rare occasions where I actually saw 2 McFatAss females prostituting themselves in front of a McDonald'd Drive-Thru. They had chosen the drive-thru so as soon as they made the money, they could waddle in and get their next fix. Once they have become that addicted and desperate, the only cure is rehab =)
'Hey look, a McFatAss!'
'AW SHIT! YOU SHOULDN'T HAVE SAID! NOW THAT HE'S ROLLING OVER HERE!'

'haha that McFatAss mom puts Dr. Pepper in her baby's bottle'

'If you want to get an Egg McMuffin, you had better hurry and get one before the fleet of Honda Civics come and the McFatAsses come to stock up!'
by Just_Jim February 11, 2008
 
2.
When Ordering At Any McDonalds The Largest Size You Can Super Size To
I Was At McDonalds And They Asked If I Wanted To McFatass My Meal;
by klosekilla August 17, 2008