Spoilers: For all episodes of the BBC Sherlock. BE WARNED.
What the hell were you thinking? Well, there was this this gif on Tumblr which emmagrant01 reblogged and of course the song popped into my head, instantly matched with specific clips from 2.03, and I had to get it out of my head because, really, do you want Jim Moriarty living in your head?
Summary: Do you know the song? Okay, then! That's the summary! :D
If the embedding doesn't work, you can also watch it here on YouTube. It was on Megaupload, which was killed the day after I uploaded it. No coincidence, I'm sure.
Notes:
This vid was completely and utterly inspired by the macro found at http://singersalvage.tumblr.com/post/15910725384/screencap-from-cumberpatches