BumCum is after your partner has ejaculated in your ass, and then Cum starts dripping outa his ass hole.
Cum Bumunknown. The act of taking a jizz on a woman's ass while she's still wearing her pants. The result of the man's unwillingness to wait for sex with his old.
That being said, however, I feel like men's bums can't be so different and so If they do cum inside your bum, you will need to go to the toilet.