You can stop worrying who the villain in Men in Black III is going to be: I've got your answer. According to the Heat Vision blog, Flight of the Conchords' Jemaine Clement will take the part, playing Boris, the evildoer once rumored to be named after a contraceptive/British band:
“Flight of the Conchords” star Jemaine Clement is in final negotiations to play one of the villains in Columbia’s “Men in Black 3.”
Most of the action is taking place in 1969, with Josh Brolin playing a young Tommy Lee Jones, who will bookend the movie.
Most of the new casting will be the villains, whose identities, look and super-abilities are being kept under lock and key. It is known that Clement is playing a villain named Boris, who is described as being charmy and creepy at the same time. (The name Yaz was used as a filler name, and since the script is still being polished, there is a chance the name may change again.)
Remember how the first Men in Black ended with this elaborate zoom back to reveal that our entire universe was inside a marble being played with by a strange alien child? Which gives more perspective to your place in the universe: that shot, or the fact that this film is happening and will make $300 million?