[JarQ]

That's pretty awesome.

Would be kind of epic if someone staged something like that in some rural town just to mess with the locals lol.

[Harvey]

Not the best once I've seen, but still pretty cool. Wouldn't really call it a flash mob either.

[Halon2]

I think a lot non-participants had a "WTF" moment when they started to high-fived by people.

[thechubbygod]

Improv everywhere does a lot of cool things like this. I once saw a video by them where they got a bunch of people to wear blue polos with khakis and walk into a best buy store. There were so many of them it was hilarious! The store ended up calling the cops, but the cops just said they couldn't arrest people for wearing blue. It was gold.