As far as I can tell, the only case where "cultural appropriation" is legitimately bad, is when people turn another culture's symbols of accomplishment into a fashion accessory. This is the case with the Native American headdress, where every feather represents a milestone or accomplishment, and Maori life tattoos, where every tattoo represents an event out of that person's own life. Turning that into your own fashion statement without any respect for the cultural meaning, is like wearing a Purple Heart you didn't earn, except that that purple heart doesn't have the same spiritual/cultural meaning.
But stuff like yoga, jazz/hip-hop, or even food? There it turns into an argument for cultural segregation, where minority cultures are effectively not allowed to become mainstream.
Exactly, I just noticed that the line of what's right and what's wrong is pretty fluid on Twitter. See some people get called out even just for eating food which isn't from their culture. Or a girl wearing an oriental dress to prom while being white. Just all things which seem to be Pro-[Insert Culture].
I'd rather have people eat food, wear clothes and hairstyles from other cultures instead of saying "I hate X-Cultures-food and/or clothing."
As you said, there are of course things which should be considered bad. You mentioned native american headdresses, which I think is a good example. But dreadlocks, cornrows? Come on....
Dreadlocks are quite interesting in this regard. If you were to consider them as having specific religious/cultural value, then they'd be specific not so much to black people, but either to Rastafarians, or to any adherent of an Abrahamic religion who has taken the Nazarite Vow, which is associated with the biblical figure Samson, and means you don't cut your hair, and abstain from alcohol and contact with corpses, and possibly a few other things.
But knotting into dreadlocks is also something that hair just does naturally if you don't comb it.
That's also a good point. Some just look at specific times in history when something was exclusive to a culture, ignoring that earlier or at the same time other cultures had the same things.
But stuff like yoga, jazz/hip-hop, or even food? There it turns into an argument for cultural segregation, where minority cultures are effectively not allowed to become mainstream.