I came across this one earlier in the week.
There are rumors that some of these people are actually professional dancers that worked with Michael Jackson (check out some of the comments below the video), but I didn't explore this fact any further.
The dancers are supposed to be max. penitentary prisoners who practiced and performed this flash mob.
Regardless of who they truly are or the reasons for doing it, I think they do a pretty good job.
Enjoy and Happy Weekend!