This is a mooninite. A mooninite is an advanced, absurdly arrogant and highly annoying creature from the Moon. They first appeared in an episode of Aqua Teen Hunger Force in October of 2001 and have since been featured in five additional shows (they showed up again for single episodes in 2002, 2003 and 2006, and in two 2004 episodes). The original mooninites episode is still probably the show's zenith (although for me, it's a toss-up between the mooninites and The Wisdom Cube).
Some people were -- and are -- highly upset about the fact that a couple of "hoaxsters" put these up in Boston (funny -- in nine other cities the people who put them up were called "marketers" and nobody got upset). Then again, some people really need to get over themselves. It's a stupid joke. Laugh or don't. But don't ask me to take this stuff so seriously.
We do whatever we want whenever we want, at all times. -Ignignokt, a moonite