This is a video of some guy demoing an Oculus Rift in a mall (Oh shit -- TGI Fridays?! I'll have the loaded potato skins!) and riding a virtual roller coaster when his buddy pushes him over right when he's about to make the first drop. He freaks out. And I don't blame him, it sucks when you realize a friend is an @$$hole.
Keep going for the video, but skip to 1:30 for the good part.
Thanks to Marcus O, who agrees you should never let somebody stand behind you when you're Oculus Rifting. Or masturbate without the door locked.