There’s a medical condition that describes someone who dances like this.
The term is amusia, a congenital condition that makes it difficult for a person to process music. While some people may have difficulty (or a complete inability) to deal with pitch and timbre, a sub-category involves those who cannot comprehend rhythm and beat, often referred to as beat deafness.
Take a look at this guy. He’s obviously trying to have a good time, but–well, you’ll see. (Via Holy Kaw)