FuckFace is a word used to define a group of people who use social media sites (such as tweeter, myspace, but mainly facebook) to show-off or go off and list what they did the whole day or tell inside jokes that nobody gives a fuck about. It's like masturbating, nobody likes it expect the person doing it.
8 year old girl: I GOT SOOOO DRUNKKK, WILD PARTY!!!!
Guy: Shut the fuck up fuckface, go draw on the pavement or something.
Annoying fuck: LOOOOL FAT GAY BUTT SEX AT THE MALL-with Fred & Dan