A spell in the 5th edition of DnD, which allows a bard to damage a creature by insulting them.
Essentially, it's a way to kill creatures using deez-nuts jokes.
DM: The dragon is bloodied and seems like it's on its last points of health. Bard, you're up.
Party: Please, don't use Vicious Mockery...
Bard: He fat.
Dragon: dies.
And that's how we stopped playing DnD.