Generally, to screw someone or something over, or otherwise mess things up (such as plans or a game). Can be used interchangeably with Bullshit.
Darren: Hey man, I'm on our way
Madonna: Oh, well I'm about to leave
Darren: What? You said you were gonna be there for awhile
Madonna: Yeah but I got bored
Darren: This is some FNS, man
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