Etymology
From being an epidemic spreading through the gay community.
Noun
gay plague (uncountable)
- (pathology, obsolete, slang, 1980s) Synonym of AIDS (“acquired immune deficiency syndrome”)
1989, Marshall Kirk, Hunter Madsen, After the Ball: How America Will Conquer Its Fear and Hatred of Gays in the '90s, Doubleday Books, page xiii:And it aims to launch upon this task in an era of superlative need and supreme difficulty, the frightening era of ‘the gay plague,’ AIDS.