The sixties marked the transition in the predominant meaning of the word gay from that of "carefree" to the current "homosexual".
In the British comedy-drama film Light Up The Sky! (1960) directed by Lewis Gilbert about the antics of a British Army searchlight squad during World War II, there is a scene in the mess hut where the character played by Benny Hill proposes an after dinner toast. He begins, "I'd like to propose..." at which point a fellow diner, played by Sidney Tafler, interjects "Who to?", suggesting a proposal of marriage. The Benny Hill character responds, "Not to you for start, you ain't my type". He then adds in mock doubt, "Oh, I don't know, you're rather gay on the quiet."
By 1963, a new sense of the word gay was known well enough to be used by Albert Ellis in his book The Intelligent Woman's Guide to Man-Hunting. Similarly, Hubert Selby, Jr. in his 1964 novel Last Exit to Brooklyn, could write that a character "took pride in being a homosexual by feeling intellectually and esthetically superior to those (especially women) who weren't gay...
In recent years, however, this traditional sense of gay has been driven out of the language by the newer sense meaning homosexual. Many believe this new sense of gay to be quite recent, when in fact it dates at least to the 1920s and perhaps even earlier. This early existence is as a slang and self-identifying code word among homosexuals, only entering the mainstream of English in the late 1960s.
Gay meaning ‘homosexual,’ dating back to the 1930s (if not earlier), became established in the 1960s as the term preferred by homosexual men to describe themselves
So, as I said, by 1964 the use of "gay" to mean homosexual was well established in the homosexual community and creeping into the mainstream. The lowlifes who broke into Mrs Hilyard's house would be expected to be familiar with dodgy slang; their use of it was meant to make the scenes even more sordid. Whether everyone in the audience got the reference is another matter. No doubt some did not, but certainly some did. The point is that it is simply wrong to assert that "gay" for homosexual was not in use by the time this film was made.
Key word: TRANSITION. If it meant strictly homosexual, it wouldn't have been used in a song in 1961 to mean happy. Mad Men also uses it to mean happy. Calm down and accept that people disagree with you.
LOL at "calm down." If I were any calmer at the moment, I'd be asleep.
You complained about a lack of sources; it was a reasonable complaint, so I provided sources.
Yes, the word was in transition. If you read back over the thread, you'll see that we are saying the same thing.
Be careful calling Wikipedia a source...unless you've double-checked the footnotes.