John Mayer friends with the Joker

So John Mayer is a singer/songwriter who's had a couple of hits, and is responsible for playing the fight riff that makes white people fight (according to Dave Chappelle). It appears that he is also friends with the Joker, as he was the recipient of some goods from the Clown Prince of Crime. According to Mayer's blog Honeyee, Mayer received a package from Gotham Novelties, Inc. The box also has a rather familiar tagline "Why so Serious?" Within the box there lay a Joker card, as well as a pretty spiffy T-shirt. Holy marketing savvy Batman. The Joker is marketing himself. John Mayer+Joker=BFF