Watch Jimmy Fallon and One Direction Sing ‘Santa Claus is Coming to Town’ [VIDEO]

What happens when you put the world's biggest boy band in ugly Christmas sweaters, hand them toy instruments and shove them into a closet with a late night host and The Roots?  You get one of the coolest renditions of 'Santa Claus is Coming to Town'.  Watch One Direction duet with The Tonight Show's Jimmy Fallon for another classic clip.