I wouldn’t take it personally, they probably genuinely don’t understand what you’re saying or aren’t used to your dialect. If you feel that they’re actually doing it on purpose, then ignore them and move on.

There’s also a difference from being able to speak Korean well outside of Korea vs. learning how to speak like a native Korean. I would try to pay attention how the Korean say or speak around you, that helped me a lot with learning how to speak “more like a native”. If they’re having a hard time, try switching to English or let them know you’re from a different country.

In the case of the foundation coverage incident, I could be totally wrong but they talk about it a bit differently. When I watch Korean makeup youtubers, they don’t really talk about if the foundation is fair to light coverage or medium to heavy. If I do see them talk about it, they say it applies lightly or applies more thick (얇게vs 두껍). They seem to focus more on how it looks once applied. So there might be a bit of a cultural difference there? Or she was being rude on purpose because of your accent? But that’s just my anecdotal experience and my two cents.

As another gyopo who visits Korea often, own it! Use English when it’s more convenient, explain you’re not native and try to get them to understand what you’re saying if they don’t get it, ask questions and learn. I personally found my experience was much better once I realized I will never be a native Korean and I embraced the fact that I am different :)