Filling one's mouth with liquid and clapping the cheeks together to emit a misty spray of liquid into another's vicinity, like a fire-breathing dragon. Seems to have originated at small liberal-arts schools in the Northeast, possibly Dickinson or Middlebury College.
Dude One: "Bro why's your face all wet?"
Dude Two: "Some punk just clapped his cheeks together, and his eyes got all wide and he yelled "Frat Dragon!" in my face.
Dude One: "You got Frat Dragoned"