Euphemism treadmill

The euphemism treadmill is the idea that even when people use nicer words and polite language to talk about something, those words can eventually become negative. To explain with an example: let's say someone wants to find a way to talk about bad people without using mean words. They might say "they are mischievous" instead of "they are bad". But over time, because everyone keeps using the same polite language to describe these people, "mischievous" will become an annoying word that makes people think of bad people. So you have to keep changing the words you use, or else the polite words will start to have a negative meaning. That's the euphemism treadmill!