Cash me ousside, meaning "catch me outside", is a term meaning to go outside with someone and fight them, rather then doing it inside where they will cause too much commotion.
Billy: Cash me ousside howbow dah
Tommy: Ok let's go fight!
Sarah: Your so stupid looking in those uggs, yoga pants, crop top, and choker.
Hannah: Cash me ousside howbow dah
Sarah: Ok let's go! I just got my stiletto nails sharpened.