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.
A driven group of individuals that are so ambitious that one may think of them as a fool.
A "Foolie" is one who has outlandish dreams, one who is willing to take unusual risks and one who goes the extra mile for that which may seem to be unattainable.
Alexander the Great was a foolie for chasing his outrageous goals.
Those young men are foolies for trying to become famous.