Single Ladies Single Man Beyonce Mashup is a video of Youtube's Dancer554 doing the exact choreography from Beyoncé's Single Ladies video, played concurrently with the original Single Ladies video. This video was once up on Youtube, but has since been taken down due to a copywright claim by the Warner Music Group.
The manorexic dancer is amazingly spot on. It's crazy.
The non-mashed up video of Dancer554 doing the dance solo currently has over 1,924,841 hits, which means you were probably forwarded that version a long time ago. And when you clicked on the link you saw a Youtube notice that said, "This video or group may contain content that is inappropriate for some users, as flagged by YouTube's user community." Wtf. While I think that is some insane ribbage and insane dancing, it doesn't really merit a parental advisory.
Anyway, the dance is cooler with the synchronized video. There is also another similar but fuzzier video that shows some suspiciously simlar Bob Fosse choreography as an inset. That, or the abominable snowman, I'm not sure.(From Thomas / Kristin's Facebook way back in November, because Stef mentioned it at the Schmitzvah.)