Any mannerism made by Ryan Heite.
Ryan (FOSK): I totally got to third base with her when this big bull cam up and rammed me. It's ok, I killed it and fed it to my tame lioness, Shiba.
An acronym which means Full Of Shit Kid.
A FOSK is someone who constantly tells stories about their life to strangers, even though the stories are false. The stories can range from hooking up with a mass number of girls to knowing the name of every star in the sky.
This word is usually used to talk about the said person in thier presence.
Everyone knows FOSK is lying when he says he's not a virgin.