Gaylords Say No
In less enlightened times, homosexuality was illegal. However, with this essentially being a private activity, it was hard for police to secure convictions, and it was for this purpose that a test was devised - the suspect would be asked a simple yes/no question, whather they had watched a film last night, 'Gaylords Say No'. As there was no such film, most people would answer "no", thus proving themselves to be a gaylord. The question was something of a double-edged sword, as even an answer of "yes" would raise suspicion - after all, why would you watch a film with such a provocative title? Many notable people were convicted by this test, including Oscar Wilde.
Eventually, homosexuality was decriminalised, and the test fell out of official use, but has lived on in school playgrounds, notoriously illiberal places. It was here that Ricky and Steve would likely have learned about it, and it is something they have incorporated in many of their works.
The test was used on Karl and then explained in the episode of 17 November 2001. Karl, as per usual, misunderstood the joke and proceeded to ask Ricky "Did you see that Gaylord film last night?", thus rendering the gag useless. It also made an appearance on The Office, with Tim asking Gareth if he'd seen that film last night. An earlier version can be seen in the DVD extras where Tim is trying to teach the cleaning lady the joke to play on Gareth but, like Karl, she can't seem to get it right.