A Strawman chaotic evil character is a villain who goes out of their way to hurt the innocent as much as possible, even if it gains them nothing or puts them in danger, simply because "mwahaha I'm evil and I like it". The trope is an inaccurate portrayal of evil; people in real life do evil things, but only when it gives them something they want. There's no such thing as a positive desire to be evil.
But also, I think it's very destructive. Portraying evil as a senseless, incomprehensible thing divorced from self-interest harms our ability to understand the causes of real evil and how it can be fought. The lesson learned by everyone who practices most forms of authoritarianism (in the rare event that they do learn it) is that you cannot change behavior without understanding it.