Question Author
So it's rather looking like nobody else remembers the thing that my memory is telling me that Kenny Everett used to keep playing on the radio in the 70s?
In the meantime, since I first posted the question, I mentioned this to a friend of mine, and got a response of recognition that I wasn't expecting: she said that it was one of those things which kids back then kept trotting out as a kind of standard humorous riposte, i.e. Kid 1: 'You're not going out in this weather, are you?' Kid 2: 'It's alright, it's not too bad, it'll be OK'. Kid 1: 'Well, you're a better man than I am, Gunga Din'. But I don't recall ever hearing that said by any of my school mates (although by the mid-70s, I was well past school age!)
But I'm still certain that Kenny Everett used to keep dropping this into his radio shows every so often, and ending up in gales of laughter.