Roxy Richter is apparantly about to win the fight against Scott Pilgim and she says those words to her ex, Ramona Flowers
"Your BF's about to get F'd in the B"
BF is obviously boyfriend. F'd in the B could mean a couple things, and it seems like it should be obvious, but it doesn't google or urban dictionary and I'm not sure what F'd in the B means. F'd in the A has meaning and that urban dictionaries. F'd in the B doesn't.
If F is a curse word, and I'm thinking it is, just type f**k or something like that but it could also mean foot. And, yes, this feels like a dumb question with an obvious answer, but I honestly don't know what it means.