In this video, a variety of scientists are asked this simple question: "If I put my hand in front of the beam at the Large Hadron Collider, what would happen?" Their answers are all over the map, but generally they agree that it's not a good idea.
A few sample answers: "Don't know."; "Not a good idea. Wouldn't recommend it."; "Gosh. Um. I don't think you'd feel very much."; "It'd probably be very bad for you and they'd be very cross with you."; "That synchrotron radiation is very nasty!"
Note: after the first four minutes, this video gets into other topics that aren't quite as amusing, but still worth a look.