Acronym. Fuck Me Sideways With A Concrete Barge Pole.
Commonly used to express that what you are about to say is important, relevant, or otherwise unbelievable.
a) FMSWACBP I wish China would stop fucking around!
b) You can't be serious, FMSWACBP!
c) Your mum is hot, FMSWACBP
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi