I had a friend slap a knife out of a dudes hand by accident at a gas station once. The way he tells is, he was in line to pay, guy in front of him pulled a knife on the cashier, friend made a "oh shit" noise, guy turns around, friend drops his shit and somehow simultaneously knocks the knife out of the guys hand while clumsily trying to raise his own hands in a "don't stab me" guesture. Knife dude was running for the door before the knife hit the floor.
Friend got all the praise for saving the day, but he lets us know it was all a nat 20 luck roll and divine intervention from a trickster god.