A top 5 seems kinda ridiculous, but I'll highlight the example of appropriating Indigenous culture just because here in Canada the Indigenous are kinda our "black people", and we've tried to eradicate their culture as much as possible for pretty much the entirety of Canadian history. The danger associated with cultural appropriation is how it changes the significance of Indigenous idols, customs, and symbols in a veiled manner-- thus stripping the significance of said things. That's why some are so scared of appropriation-- when you're forcing assimilation, it's very very overt. Appropriation meanwhile has the potential ability to eradicate cultural meaning covertly. When you're bringing Indian headdresses to raves, or rocking mohawks at punk concerts, it loses meaning. And unfortunately, it's usually white ppl who are the appropriators.
This sounds meaningless to you, but that's because you've never been had your culture questioned, or attempted to be robbed from you. Talk to an indigenous individual, or a person who feels like his/her culture is being appropriated. You'll develop a better understanding.