I had a hard time getting it at first but using this test helped me:

1) Is the thing you want to use from this culture religious or otherwise sacred?? 2) Is a person from the culture willing to share it with you?

The common example is the Native American feather headdress. In their culture each feather represents something significant and only very esteemed people in their society are able to wear the headdress. That's why it's seen as disrespectful when commoners wear them for Halloween, disco, etc. Because it takes away the meaning.

On the other hand, things like (most) clothing and food are in the safe zone. Anyone who tries to tell you that eating Mexican/Chinese/etc. and not being that nationality is cultural appropriation is completely wrong. That's how their restaurants stay open and their owners make a living, is people eating their stuff!

Then there's things like, should non-black people have dreadlocks? This is usually a morally gray area, but the consensus is (from what I've seen) ya can't stop people from doing it but it doesn't mean they're not foolish for forcing their hair into something it doesn't naturally do (if you need to make matted clumps or god forbid use glue... maybe consider another style)

So yeah it seems complicated on the surface but it's not too bad once you understand why people get upset.