If you grew up in a country outside of the USA, being black is mostly a phenotype as cultures are more specific to ethnicity. You are black if, by looking at you, you appear to be a person of sub-Sahara African descent. You did not grow up with the one drop rule which means that, if you are mixed in any way, you are not considered black, you are mixed race.
It unsettles me when mixed raced people with "black" heritage class themselves as black because, a) it is disregarding the other parts of their heritage, b) phenotypically mixed race people are NOT treated the same as black people and c) it upholds the Jim Crow "One-drop rule", which I believe we should be actively working against. Also, people who are mixed race, but without black heritage, are not made to "pick a side" e.g. a person of Irish and Indian descent would describe themselves as mixed, not either or (I've tested it several times).
Another pet peeve of mine is when people say things like "I identify as black." because, for those of us who are phenotypically black, there is no option to identify as anything other than black. Being able to "pass" and having the option not to, is a privilege that black people don't have; choosing whether or not to be a part of the black struggle or whether to be subject to the negative stereotypes associated to black people, is not the reality of existing while black.
Despite having lived in the US for several years, it was through a huge debate on Twitter that I learned that many African Americans used the term "black" to signify a culture (African American) rather than a phenotype, like the rest of the world do. This provided a bit of clarity on the ability to identify with it but, it has allowed people like Rachel Dolezal to exist which cannot be good.
Of course you can label yourself as you wish, I think I'm just salty that there are people who can share in the beautiful experience of being black without all the hardship that comes with it. The fact that they can "opt out" just doesn't sit right with me. This video by Tarek Ali perfectly expresses my thoughts on this.
As Tarek said, you can call yourself whatever you want, I'm just here to have a conversation. #NotRudeHonest