fat butt from eating too much fast food. not to be confused with badonkadonk, which is pleasant and attractive.
"check out that that chunky bitty on the hover round scooter. what a McDonkadonk on that ho."
A McDonkaDonk is a person who has a large butt due to eating excessive McDonalds. ; A person who was not born with a large butt, but grew one due to eating excessive McDonalds.
"I was trying on my jeans the other day and my McDonkaDonk would not fit in them so now they do not fit!"
"You better stop eating at McDonalds or you will get a McDonkaDonk girl!"