Something you say to a dog to calm them down; you may have to replace "MJ" with the dog's actualy name.
Originated from when I was playing with my sis's boyfriend's dog (which is shortened to the initials MJ). Then I said that cause I was bored and she was trying to jump on me.
Me: Mary, stay down!
*dog is jumping at me*
Me: Yo MJ what up dog?
*she stops jumping at me*