"Men in Black" were an unusual feature of the North American UFO scene in the early years, and have not completely disappeared. Dressed in dark suits, and driving black cars, they would descend, usually in pairs, upon UFO witnesses or investigators, making unspecific threats which were never carried out. One suggestion involves investigators/witnesses accidentally crossing paths with government agents undertaking investigations of their own. Add a certain degree of paranoia, and a cultural myth has started. It sounds plausible, but I shall leave it to those more familiar with the subject than I. Nevertheless, once in a while a well documented case turns up which is really, really strange.
