Q: Ok, so I’m really bad at being PC. Why is it bad if you dress up in other races’ traditional clothes? … what’s wrong with wearing a poncho and a sombrero on a day where you can be whoever you want?
Here’s why I find it distasteful. When you dress in a poncho and sombrero, you’re not dressing as an actual thing. You’re dressing as an icky stereotype some white people have about non-white people, and pulling (inadvertently, perhaps!) a whole lot of ugly backstory in your wake.
Part of being a grown-up is being polite and sensitive to those around you, and cognizant of the fact that just because something doesn’t hurt you or your friends’ sensibilities means it’s not really offensive to some people.
Don’t get me wrong: there is no law against dressing as people of other races. You can do it, if you want! The PC police will not bust down your door and arrest you. But some people will think you’re an asshole.
If it helps, don’t have to think of it in terms of political correctness. Think about it in terms of politeness, and decency. People who are kind and decent avoid actions that hurt others unless there’s really good cause. And what’s the cause here? Just go as a jellyfish.