by 1996, from metropolitan + -sexual, ending abstracted from homosexual, heterosexual. Wikipedia defines it as "a portmanteau of metropolitan and heterosexual, coined in 1994 describing a man who is especially meticulous about his grooming and appearance, typically spending a significant amount of time and money on shopping as part of this."
Nevertheless, the metrosexual man contradicts the basic premise of traditional heterosexuality—that only women are looked at and only men do the looking. Metrosexual man might prefer women, he might prefer men, but when all's said and done nothing comes between him and his reflection. [Mark Simpson, "It's a Queer World," 1996]