I'm betting the psychologists have probably figured this out by now: guys need a space. A special space. A clubhouse, a workshop, a pub, a lounge chair, an office, whatever...men are simply wired to seek a spot for themselves that energizes them.
Of course, moving beyond the way-to-old-to-be-safe-and-most-likely-smelly furniture and the vintage metal signs look isn't always easy. But that doesn't mean a man room has to be done up only in the colors of a sports team or feature multiple neon beer signs.