When someone tells an unbelievable story others in the room may secretly tell others that the story is bull sh** by saying yellow shark. The teller of the story will have no idea that everyone knows the story is false if he does not know of the word's meaning.
Joe: Dude I totally got laid last night by twosuper models!
Steve: Lemon shark.
Frank: Totally a lemon shark.
Joe: What is a lemon shark?
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)