Metrosexual Thread Humper is taken from JR Ward's "Black Dagger Brotherhood" series of books. It refers to a man, who without actually being gay, has the expensive taste for high-end clothing most often associated with gay men.
man #1 - "Look at these awesome deals on sweaters at Gucci and Versace. I'm wearing the Louis Vuitton socks and underwear I bought after my mani/pedi."
man # 2- "dude, you are such a metrosexual thread humper