Here's one I liked from Quora: A mathematician gets tired of being mocked by his physicist friends for studying useless things. He decides to go out and listen

Here's one I liked from Quora: A mathematician gets tired of being mocked by his physicist friends for studying useless things. He decides to go out and listen to the most useful mathematical talk he can find. After looking through the schedule, he settles on a talk about "The mathematics of gears"--after all, gears are useful for all sorts of machinery! It's hard to find something more practical. So when the talk comes around, he's there early sitting the front row. The grey-haired professor walks up to the front and begins: "so, the theory of gears with real numbers of teeth is well understood..."