The shit that one takes after eating hot buffalo wings. It is characterized by the burning sensation within one's anus. The butt napalm is caused by the heat of the sauce being retained through the system and causing a similar heat sting as experienced when initially ingesting the wing. The only relief for this sensation is by completing the shit, and wiping thoroughly to clear the butt of said napalm.
Man, those Caribbean Jerk wings were awesome, too bad I'm gonna have butt napalm later.