The sexual activity of smearing ketchup,big mac sauce or mustard on the reciepient's ass cheeks until getting desired distribution. Then the ass is eaten by the other person involved in the Big Mac. Additonally, the ass cheeks can be licked off as well.
This position is also known as "The Don Gorske
Her ass was looking so thick dude, I had now choice than to give it the Imitation Big Mac.