What's Up With the Title?
Sometimes movie titles straight up tell you what to expect. For example, the title Thelma and Louise informs you right away that you'll be watching a film about two women named Thelma and Louise. Butch Cassidy and the Sundance Kid is about two outlaws named (surprise) Butch Cassidy and the Sundance Kid. Lincoln is about Abraham Lincoln, but Abraham Lincoln: Vampire Hunter really is not. The subtitle helps you distinguish between the two by headlining the schlock.
In the same way, Men in Black tells you the film is about dudes who dress in black. If you're familiar with the conspiracy theories, then you'll know right away that these guys are working for the government and are assigned to cover up all evidence of alien activity on Earth.
While the title is upfront about its premise, it's also very nondescript, evoking an air of mystery. If you aren't familiar with the conspiracies, you might wonder, "Who are these men? What do they do that requires them to dress in black? Are we talking black black or jet black or more of an onyx shade?"
Mysterious is the right tone to set for a movie about a secret government agency working the in shadows to cover up signs of extraterrestrial activity. The delight of the movie is discovering the quirky answers to the questions posed by the title.