Men in black in the US, dark-clothed men of unknown identity or origin, who supposedly visit those who have seen a UFO or reported an alien encounter, in order to suppress any public account of the incident.
men in (grey) suits powerful men within an organization who exercise their influence or authority anonymously.
men in white coats humorous term for psychiatrists or psychiatric workers (used to imply that somebody is mad or mentally unbalanced).
so many men, so many opinions proverbial saying, late 14th century, meaning that the greater the number of people involved, the greater the number of different opinions there will be. The saying is found earlier in Latin, in the work of the Roman comic dramatist Terence (c. 190–159 bc), ‘Quot homines tot sententiae: suus cuique mos [There are as many opinions as there are people: each has his own correct way].’
See also be all things to all men, the best of men are but men at best, dead men tell no tales, good men are scarce, man, Merry Men at merry, nine men's morris, Three Wise Men at three, young men may die.