Passing jests passing into meaninglessness

This was in the Globe and Mail's Social Studies section today. I know it's an 80-year-old gag, but I don't understand it at all, and doubt I would even if I had another eight decades to think about it:

From The Globe's Passing Jest of Nov. 17, 1923: "He -- 'This cold weather chills me to the bone.' She -- 'You should get a heavier hat.' "

Has humor changed so substantially over the last eighty years as to render this meaningless to modern ears? Or was this a really lame gag to begin with? Or have I completely missed the joke? If someone can explain this jest to me, I'm all ears.