"Are you coming, or not?"
"Are you going to support my cause, or not?"
"Do you like Christmas, or not?"
"Do you believe in Santa, or not?"
To me, sticking "or not" on the end of a question quite strongly implies aggression, or demanding an answer RIGHT NOW. I know somebody who does this in conversation all the time, probably innocently, with questions such as "did you go to the shops, or not?" "Did you win your game, or not?" To me, the "or not" is redundant, and sounds like aggression, and implies that only a binary yes/no is wanted, and nothing more, and certainly not a longer answer.
YANBU - "or not" is aggressive
YABU - "or not" is not aggressive