Not just anyone who raps can get away with calling an album R.A.P. Music. As if Killer Mike didn't show enough on that record, one of 2012's best, why he's the guy he can do it, the Atlanta MC made it thrillingly clear last night on Late Show With David Letterman. And if you saw him at SXSW, you knew all the more that he would."New York," the longtime OutKast associate began, "you are now witnessing elegance / in the form of a black elephant." On his rendition of percussion-rattling "Untitled," though, he roared and prowled more like a supremely amped lion. Guest vocalist Scar, exhorted along by Mike, nailed the song's Old Testament-shadowed hook. Rapper-producer El-P, who produced the album, was also there as part of the six-strong backing ensemble.The last time El-P did Letterman, it was for a similarly fiery performance, which happened to fall on the same day Mike released R.A.P. Music. At the time, El-P shouted out his condolences to MCA and Maurice Sendak. Last night, though, the icing on the proverbial cake wasn't Mike's mid-song embrace of El-P — though that was hugely endearing — but at the end, when the Southern rapper gleefully wrapped his arm around the much more petite Letterman. The host smiled awkwardly, but like everyone else, he couldn't deny the moment.