What would you do if this happened to you?

So my friends and i were at lunch, and our table is right behind the dorky table (we sit by homerooms). ANYWAYS my friend was eating her mashed potatoes. (she sits with her back facing the dorks) She got up to go get a napkin. When she came back, my other friend who sits across from her flung a glob of er/potatoes at her, but she missed! It flung behind them, and hit this kid in the back of the head. He didn't seem to notice, and we were all laughing really hard. So she grabs a napkin, and starts trying to clean it. He just stares at her, and then gives her the evil eye when he found out what she did. IT WAS SO FUNNY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Maybe you had to be there for it to be funny, but what would you do if someone flung er in your hair?