“God made Adam and Eve, not Adam and Steve”

“God made/created Adam and Eve, not Adam and Steve” has been an anti-gay slogan since at least 1977. The saying has been on T-shirts and bumper stickers.
 
“It’s Christmas Eve, not Christmas Steve” and “It’s New Year’s Eve, not New Year’s Steve” are related jokes.
 
   
Wikipedia: Adam and Steve
“Adam and Steve” is a phrase that originated from a conservative Christian slogan “God made Adam and Eve, not Adam and Steve”, intended to concisely summarize Judeo-Christian Bible-based arguments against homosexual practices or homosexuality. Among other things, it implies that the natural way of life for humanity is illustrated by the Biblical account of the creation of human beings as a male-female pair.

The phrase appeared, on a protest sign, as early as 1977, as mentioned in a New York Times news service report about a November 19 rally in Houston that year. Two years later, Jerry Falwell gave the phrase wider circulation in a Christianity Today report of a press conference he had given.

20 November 1977, New York (NY) Times, “Equal Rights Plan and Abortion Are Opposedby 15,000 at Rally” by Judy Klemsrud, pg. 32:
The particpiants, many ofthem couples with small children, carried signs reading “E.R.A Is a Turkey,” “God Made Adam and Eve, Not Adam and Steve,” “IWY, International Witches Year,” “Jimmy, We’re Here, Too” and “Not Gay, But Happy People—Happy,Texas.”
 
Google News Archive
15 October 1979, Calgary Herald, pg. A21, cols. 1-4:
50,000 march for gays’ rights
God did not creagte Adam and Steve,
evangelist counters in prayer session

WASHINGTON (AP)—An estimated 50,000 homosexuals, bearing banners from nearly every state, marched through the U.S. capital Sunday, demanding civil rights protection.
(...)
Attheprotest prayer session, Rev. Jerry Falwell, a television evangelist from Lynchurg, Va., said Christians country-wide prayed Sunday for homosexuals, “askingthe Lordto deliver them from their lives of perversion.”
 
“God did not create Adam and Steve, but Adam and Eve,” said Falwell, who labelled homsexuality “an outright assault on the family” and likened homosexuals to bank robbers, thieves and other sinners.
 
11 November 1980, New York (NY) Times, “Falwell Warns Jersey Liberals AtCapital Rally” by Joseph F. Sullivan, pg. B2:
Looking over the crowd of 1,000 onlookers to a number of demonstrators holding signs aloft that identified them as homosexuals, Mr. Falwell said that in the Garden of Eden, “God created Adam and Eve, not Adam and Steve.”