In High School - 11th or 12th grade. I dresses up like this for Halloween (It's flour and water paste):
Conspired with a friend, as a Halloween prank, to scare the snot out of a girl we knew. My friend arranged a "date" with this girl and picked her up in his parent's Ford station wagon. What she didn't know is, while she was getting into the car, I was climbing up onto the luggage rack from behind the station wagon.
Friend proceeded to drive with her out into country on a lonely dirt road (with me hanging onto the luggage rack for dear life). They started talking about different urban legends and at some point he asked her if she had ever heard about the "Albino Man" who was alleged to have died some horrible death in the vicinity of where they happened to park...(you know where this is going, don't you?).
Just about the time she was getting good and scared about the Albino Man story, I dropped down and appeared in the front window, slamming my hands agains the glass and letting out a blood curdling scream!
What I hadn't calculated was that she, sitting on a bench seat next to my friend, would freak so bad that she would drop the still-running car into drive and mash on the gas! The car started slipping all over the place on the dirt road and I fell off just in time to see the car speed about a mile down the road before my friend could get it under control (I didn't get hurt - much).
Needless to say that girl never spoke to either of us again.