The point of appropriation is adopting something and using it for something other than in the way its unintended to the culture or offensive to the culture.
Wearing a Sari at your Indian friends traditional Indian wedding
Wearing a sari as a halloween costume
Wearing a Sari at your Indian friends traditional Indian wedding

Wearing a sari as a halloween costume

Wearing a Jamaican flag and bantu knots to celebrate Jamaican carnival 
Wearing Jamaican flag and bantu knots to a costume party

Wearing Jamaican flag and bantu knots to a costume party

Your white friends wearing asoebi to your trad 
Your white friends having an “African theme” party where they show up in African traditional outfits
Getting henna on hands at a culturally appropriate celebration like a Mehndi
Getting henna cos its edgy and cute

Your white friends having an “African theme” party where they show up in African traditional outfits

Getting henna on hands at a culturally appropriate celebration like a Mehndi

Getting henna cos its edgy and cute

Cultural appropriation does not mean “people not of a culture participating in that culture”
It means “people not of a culture taking aspects of a culture and using it not as is used within its cultural context and/or offending people of that culture”.
It means “people not of a culture taking aspects of a culture and using it not as is used within its cultural context and/or offending people of that culture”.