Someone who demonstrates decidedly homosexual proclivities, having been masquerading as a heterosexual for many years.
Ian, "Check out the hot girl with Chris!"
Kerr, "No good to him, i hear he's a quinner."
Ian, "Really? I always thought he was straight."
Kerr, "No no, he'e merely been masquerading as a straight man, when in fact he's known to be partial to a bit of cock."