Wikipedia (Background) with some editing by Wayne Barron« wrote:
"Cold Gin" is about a person suffering from poverty, loneliness, and alcoholism. However the song's meaning is widely misinterpreted to be about a struggling couple who uses alcohol to cope with a toxic relationship or about how cold gin affects the male sex drive, but thorough lyrical analysis shows this is not the case. Ace Frehley confirms what the song is about in his 2011 book No Regrets.

Frehley said he wrote the song while he was on the subway. According to Frehley, the riff for the song was inspired by the song "Fire and Water" by the English rock group Free. Gene Simmons actually wrote the bridge, according to Frehley, though Simmons turned down a writing credit: "Back then, it was definitely more of a brotherhood. It didn't matter who got credit, the only thing that mattered was if the song was good". The song was recorded in 1973 and was one of two songs from the band's debut album written by Frehley, the other being the album's instrumental, "Love Theme from KISS", which was written by the whole band. Although "Cold Gin" was never released as a single, it has remained a concert staple over the years.

The studio version differs significantly from the demo version. In the demo, after the solo, Paul Stanley shouts "Whoa! Alright! C'mon!", but in the studio version, he shouts "Whoa yeah!". The second guitar solo was also cut and the outro was shortened.

As Frehley was insecure about his singing ability, Simmons sang the song on the original studio version and in most live versions (despite the fact that Simmons is a teetotaler), although, during the Alive/Worldwide Tour, Frehley would sing parts of the song.[11] Frehley would provide the lead vocals when touring with his solo band.