Carmelldansen is actually the name of a song performed by a swedish group that goes by the name of Carmell. The song was later remixed into a speedy techno version that became a meme after someone made a video of two anime characters from the series Popotan doing some weird bouncy dance to it. The whole video has become a meme with characters from other series doing the Carmelldansen dance. ....Or, you can just check out the Wikipedia article and the TvTropes page.
