Men in Black (MIB),is a science fiction action comedy film, like popular culture and in UFO conspiracy theories. In this movie men dressed in black suits claiming to be government agents, who attempt to harass or threaten UFO witnesses into silence. Sometimes implied that they may be aliens themselves. Frequently used to describe mysterious men working for unknown organizations, as well as to various branches of government allegedly designed to protect secrets or perform other strange activities. The term is a generic one, used to refer to any unusual, threatening or strangely behaved individual whose appearance on the scene can be linked in some fashion with a UFO sighting.

http://www.imdb.com/title/tt0120912/