I stole this one from joystiq.com, so I’ll just copy-paste what they wrote. Really scary, but really funny, short video.
There are few words one could use to describe the audio phenomenon which occurs at each Penny Arcade Expo, other than, of course, yucky. The video posted after the jump was captured at the first Penny Arcade panel at PAX East, in which everyone in the room simultaneously cracks their knuckles. It is really, really gross and nobody should watch it. We wish we hadn’t seen it. We also wish we hadn’t filmed it, and then copied it to our computer, and put it online, and put it in this post — a process forcing us to relive that horrifying moment eight or nine times.