go get some preparation H. relax. "these degenerates of america..." oh for Christ sake... it was a damn FOOD FIGHT. can you think of worse? I can...how about people welding doors shut or shit like that? Anyways, if the cafeteria's anything like my old high schools, it's got a high ceiling so nothing gets stuck to it, and the walls are layed out in a manner that would (yes) allow pressure washing...
On another note, and this was not intentional, i got chocolate milk all over a principal's shirt/tie. i had a half empty carton and i threw it at the garbage can the principal was wheeling diagonally towards us, i led it wrong, and it bounced off the back rim of the can and splashed...no points for smoothness there!