FMF

Short for filthy mother fucker. Usually used to express disgust towards a person. Pronounced: Eff-emm-eff

Guy 1: Hey did you do rigorous activities this weekend?
Guy 2: FMF.

Rigorous activities

Referring to either the act of sex or calculus depending on the circumstance. Sometimes purposefully ambiguous.

Guy 1: I did a lot of rigorous activities over the weekend.
Guy 2: Really?
Guy 1: Yeah, but I'm still screwed for the calc midterm.

FB

Short for fucking bitch. Usually used without an accompanying sentence. Sometimes used to insult someone without them knowing. SPronounced: Eff-bee

Guy: Do you want to go to prom with me?
Girl: No, so stop asking me every day.
Guy: FB.