Meaning there is no reason or justification for something; A substitute for saying "No Reason"; (Taken from the popular Apple Jacks cereal commercials, in which the characters couldn't give a reason for their liking of Apple Jacks cereal.)
"Why are there three lesbians and a republican in the living room?"
"Its Apple Jacks"
"Why are you still here?"
"'Cause I am"
"Don't Apple Jacks me!"