The huge secret is that "fsck right off" was intended as jokingly rude, English is not my first language.

Though this may be irrelevant since even yesterday a clearly joking text was perceived as an insult by one acquaintance in one chat. I'm not sure they didn't put into this a bit of their unwillingness to accept that their own sense of humor is not the only kind allowed, but some others made the same mistake, so.