There's really just one thing, but it covers a lot and it's driving me crazy.
Definitions.
Humans give names to things so that we can talk about them. So why can't we leave them alone?
This can get extremely political so I'll try to be vague. And that's part of the problem.
Some words get bad connotations because people use them accidentally wrong or intentionally as insults. So those become "unusable" and we have to start using other words in their place. But because it's still pointing at the same thing now the new word gets "tainted". Oooh, we can't use that, that's a bad way of saying it. So now we have to find a new word for it. Sheesh. How the hell are you going to talk about it then? No, don't say it, I get it, you don't really want to talk about it at all, you just want it to go away. Well it's not going to.
Some words get muddled by people who want to use their good reputation to their advantage. "I stand for this issue and anyone who doesn't stand for this issue is clearly stupid". Well sure, but you know what, no you do not. You are using the wrong word so that people get confused about what you are talking about. Then you go on tv and because everything on tv is true, oh look what happened now, everyone starts getting it wrong. And what ever happened to the original definition then? How are we going to talk about that now. Oh that's right, that was your intention all along. Well thanks a lot.
It's bad enough that we have a million different languages, we can't even agree to use the ones we do use concisely.