(Coloquial use Jamaica) can be used to replace modal verbs like should, must and have to when giving some advice or talking about something that is necessary to do.
my FI has huge fingers. The jeweler measured him at a 15.5 but said to order a 16 if we wanted a thicker band. My FI is 6'4" and a big guy so it makes sense.
An FI is an an abbreviation for Fucking Idiot. You see these driving on the roads every fucking day. You can also find them in the workplace, in stores, and health clubs, police departments, and yes hospitals too. Most of them are men, but some are women.