Said after something meaning it's the 100% truth. This cannot be used sarcastically, or any other -ly, except truthfully. You don't fuck with this shit.
It's origins come from South Park season 4 episode 16 'The Wacky Molestation Adventure.'
Person A: Holy shit, I just won $1,000,000 on this scratch ticket.
Person B: Bullshit.
Person A: No foolies.
Person B: Holy shit, buy me a car.
Person A: No.
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)