Castbro
A straight male in the midst of a region generally populated by gay men. Said straight male usually plays up his heterosexuality to make it apparent to others/outsiders that he is not gay, sometimes resulting in bro-like behavior.
A: "The waiter at that restaurant on Castro Street was totally a Castbro. He did not set off my gaydar at all."
B: "It's too bad - he's kind of cute."
B: "It's too bad - he's kind of cute."