An early name for AIDS due to the lesions of Kaposi's Sarcoma that often characterized the disease.
Gene: You know, I have that gay cancer... and now you might have it too.
Before much was known about AIDS/HIV, "gay cancer" was sometimes used to describe this strange infection that effected mostly homosexual males in the US.
Fag caught a case of gay cancer.
A homosexual male that is ruining potential social progress of other homosexuals. An individual considered to be gay cancer is typically looked down on by other homosexuals and almost always fits the demeaning gay stereotype.
Stella: Did you hear what Jamie was talking about in class? The professor was totally disgusted and called him the most obnoxious person he has ever met.
Mario: He's such gay cancer