We've all heard the phrase "one-joke idea", and it's invariably used as a put-down.
But sometimes a one-joke idea can be innovative and experimental writing, in addition to being funny.
This is an SCTV sketch from the late 1970s, a spoof of the old game show What's My Line, here renamed What's My Shoe Size?:
For more than half its length, this is a straight parody of the old show, with a number of jokes (such as Bennet Cerf's overflowing vocabulary) dependent at least in part on your familiarity with the original. It's more than three minutes before we get to the sketch's basic gag, the overspecific game show premise (a frequently-used technique in game show spoofs). We watch the distinguished Broadway types trying to figure out a guy's shoe size, the absurdity of the activity made even more ridiculous by the questioning process of the show.
The writers made the decision not to stress the shoe size bit, almost as if they were somehow afraid of committing to the idea. So they are careful to space shoe size gags with jokes based on the original logistics of What's My Line, some of them admittedly very funny (such as Dorothy Kilgallen neglecting to remove her blindfold when shaking hands).
What is in my opinion a much more innovative and, in performance terms at least, more courageous sketch had been done on the Peter Cook and Dudley Moore BBC-TV series Not Only But Also in 1965:
This sketch is sometimes erroneously credited to Cook himself, but it was actually written by a Cambridge classmate of his for a university revue in the late 1950s (those intrigued by Cook's personality quirks may wish to note how he seems to be almost hiding from the camera in this musical number -- compare his reticence to the enthusiastic up-front mugging of Dudley Moore).
The bit opens like a standard Robin Hood take-off. Yes, they're singing about Alan-A-Dale, but we know they'll get to the Robin Hood jokes soon. Well, eventually anyway. I mean, they are going to get to the main sketch aren't they? How long is this stupid intro going to go on???
Of course, we eventually realize, that's the whole point. I think everyone who watches "Alan-A-Dale" finally gets the joke, and then thinks, if only subconsciously: How long can they stretch this out?
Personally I think the sketch would've been even funnier, if riskier, with a standard leading man as Alan-A-Dale, rather than the comedian that was used. He would function as a stand-in for the audience, clearly in discomfort and confusion wondering when they'll get to his adventure.
I also think the bit could have been stretched out even further, with more "Alan oh Alan"s etc. But the fact that it lasts four minutes, with only a few other non-premise jokes (Dudley bumping into the lens, Alan being blocked in his entrance) is extraordinarily impressive. It's almost like a blues jam, as everyone watches to see how far the performers can go within the self-imposed limits of the material.