Bowl Burn
When a stoner takes the bowl from his or her pipe/bong and gives themself a burn mark. This is usually done by masochistic pot heads who get bored after smoking.
That gothic chick has a gigantic bowl burn on her arm.
Bowl burn
This is when your turds rubs against the bottom of the toilet bowl and creates a burn mark. Similar to rocket burns in underwear.
Dude. Your shit left a bowl burn.