yes, this is historically always how I've heard FAFO used - basically like a threat before someone does something stupid

but recently it seems like the meaning has significantly shifted, particularly in liberal communities and political contexts, to imply that people we don't like politically will get what they deserve (a bit like /r/LeopardsAteMyFace)

an example was a posts in /r/MarchAgainstNazis titled "The arc of 'F**king Around' is long, but it bends toward 'Finding Out'" (this is a remix of the Martin Luther King Jr quote)

So in a sense it's still taking on some of the threatening tones originally used, but I feel like with a lot of liberals it turns into constant cope, waiting for the criminal political actors they obsess about get the justice that is owed