Just Dance 3

First make sure 'short choreographies' are on in the options menu. Then dance (or just sit there) through 50 choreographies. This didn't pop for me after 50 though, because the game can only save 50 choreographies, and I had downloaded a choreography for another achievement. I had to delete the choreography I had downloaded, then make up another choreography, so if you have downloaded a choreography or two, delete them before you finish making 50 of your own.