A form of retaliation against someone who has wronged you in some way.
Mama Birdin' is when you chew up some food and spit it in someone elses mouth. The is especially effective if you wait for the person you're going to mama Bird to fall asleep and their mouth is open. This gives you the element of surprise.
My brother borrowed my car the other night and left me with almost not gas so I'm Mama Birdin' him tonight when he's in bed.