Friday night on Late Night With Jimmy Fallon, the lovably fired-up Mississippi rapper/producer Big K.R.I.T. trotted out his hella-fun new single "I Got This." The Roots, a band uniquely well-suited to take on K.R.I.T.'s humid organic thump, backed him up, and it was a ton of fun to hear the tuba taking on the song's subs. But the real joy ...