Wiktionary
gay dog
n. (context colloquial dated English) A womanizer.
Usage examples of "gay dog".
The two men, looking like a comedy team: one fair and fat, the other dark, red-faced and scrawny, seemed to want to play the gay dog.
Knowing me by now, the reader can easily imagine how dusty and hot I got, trying to catch a glimpse of nymphets (alas, always remote) playing in Central Park, and how repulsed I was by the glitter of deodorized career girls that a gay dog in one of the offices kept unloading upon me.