If you don't know what the Harlem Shake is, you're not the only one; it's only been around for a week or so. Then again, it exploded in that time so maybe you're just using the Internet wrong.
In any case, it's a moot point, the Harlem Shake is officially dead now that both Facebook and Google have done it.
Actually, maybe the meme could have survived that, but Groupon and Intel have done a Harlem Shake video. There's even a Today Show version with a Valentine theme.
Any minute now, a Microsoft video should surface. When that happens, the Harlem Shake meme will be so uncool you should probably be able to start doing it ironically. By the way, you're all doing it wrong anyway.
If you're interested in ancient history, the Harlem Shake meme started way back on February 2nd, recount those old enough to remember.
It took a few days for it to pick up steam, but there were 12,000 videos by February 11 which means there should be twice as many by now.