It originated from the brisk streets of london, between a small group of friends. When seeing a girl from afar that you recognise from the social network know as 'Facebook' you say they looked fitter on facebook, FOF. This has been used as an inside joke between friends so that you can't be caught out when in public and we believe its time that the rest of the world should know about it.
Ask your self this are you a FOF?
FOF (Fitter On Facebook)
What is that about, mate that girl is FOF.
She looks like she carries a heavy load, she was defiantly FOF.
That girl looks like she takes a dick, she looked FOF.