Fair warning: This is a white liberal guy talking about this issue; apply whatever salt you want to go with the post based on that.
So, if you want to talk about cultural appropriation, you can pick examples that have the plain look of "that's sensitive to the point of ridiculous". You can pick examples that have the plain look of "that's vicious and disrespectful".
Or you can address muddled cases, which is where most of the examples actually are. I'm going to talk about one of those.
Sam Phillips, who did the recording for Elvis, famously said "If I could find a white man who had the Negro sound and the Negro feel, I could make a billion dollars."; this because the recording industry wanted black music, but didn't want black people.
Sam Phillips also recorded B.B. King, Junior Parker, and Howlin' Wolf (all black artists, should you suffer the sad misfortune of not knowing their music). So it's not like Sam Phillips didn't want black artists, but he knew the score.
Elvis was where Sam Phillips made a goodly portion of that billion dollars, and Elvis was a white man who "had the Negro sound and the Negro feel".
Elvis, in turn, famously said "The colored folks been singing it and playing it just like I’m doin' now, man, for more years than I know. They played it like that in their shanties and in their juke joints and nobody paid it no mind 'til I goosed it up. I got it from them. Down in Tupelo, Mississippi, I used to hear old Arthur Crudup bang his box the way I do now and I said if I ever got to a place I could feel all old Arthur felt, I’d be a music man like nobody ever saw."
So Elvis wasn't aiming to give anybody black music without black people; he gave credit, and showed respect to where he learned what he learned. However, he did benefit from the desire of the recording industry to give the world black music without black people; if that aim on the part of that industry hadn't been present, he might well have had a lot more competition for that sound. If he hadn't been around, then we might have had more popular black artists singing their own sound to wider audiences a little sooner because the recording industry wouldn't have had the option of Elvis.
The recording industry attempted to push the rewards for black music to go primarily to people who weren't black, and that's one of the places where appropriation lives. Elvis and Sam were marginally complicit in this, but also visibly resisting and even subverting it.
Okay, now, let's jump that over to Iggy Azalea, and the general statement of "She's appropriating black music, culture, and images!". And the response to that is... Maaaaybe? I mean, do you require the potential for misrepresentation, exclusion, or erasure as part of appropriation?
Hollywood portrayal of First Nations people often includes a good deal of misrepresentation. Painting a whole group of peoples as savage or 'magic' by grabbing their culture, portraying it without them in it, and getting it all kinds of wrong, is a problem, because it fucks up their relationships with other people if it drowns out their own representation of their identity. Doing the same thing with Grimm's Fairy Tales isn't likely to have the same effect on Germanic peoples, because it's not about to drown out their own attempts to assert who they are.
Equally, the creation of tourist-trap fake First Nations artifacts for sale via factories in China, underpricing what the actual producers could potentially sell them for, means excluding them from the fruits of their own culture. Which is pretty shit; it's what the recording industry would have been happy to do with Elvis.
Finally, if you've ever seen a film where all the people of some ethnicity are played by white people, that's erasure; the actual people of the story are being wiped out of it.
Iggy Azalea's performative style is totally based on images popularised by black artists, which may be rude and silly; however, evidence that it misrepresents, excludes, or erases... is not as thick on the ground. Some, maaaaaybe? But it's not a clear or strong case.
Misrepresentation, exclusion, and erasure are all pathways to significant harm, and most of the examples of appropriation that are worth arguing over contain these things. Which isn't all the examples where people shout it, mind you; but it's sure enough that it's worth pointing at and noticing. So, when I hear the term thrown around, I look and try to imagine where those components are - the misrepresentation, exclusion, or erasure.