African American and black are two relatively neutral terms for denoting Americans with African ancestry. Both terms are used in everyday conversation in North America, and just like the broader label person of color, are safe ways out if you want to refer to someone with transatlantic heritage and particularly dark skin.
Moving on to non-neutral terms referring to African Americans, if a black man or woman is described as chocolate it is usually a way to say that he or she is yummy or sexy. In line with this, some blacks take it as a compliment to be called chocolate, and sometimes even use the word to cheekily refer to themselves. However, not all African Americans appreciate being referred to as food just because it matches their skin tone, so the word chocolate ought to be used selectively and tactfully, if at all.
Nigger and nigga
Far worse than the term chocolate could ever be perceived is the inference of the word nigger. This word is closely associated with racial hierarchy and the oppression of black people, and therefore not appreciated at all. Similar-sounding nigga, on the other hand, is used among many African Americans themselves. This term, nigga, is particularly common in black hip hop culture and among certain groups of black youth, contributing to nigga being much more accepted than the related word nigger.
Negro, which looks a lot like both nigger and nigga, was the politically correct word for African American or black up until about the 1960s. Prior to this time, blacks and whites alike referred to black people as negroes on a regular basis, with few people reacting negatively to it. Starting around the 1960s, though, as previously mentioned, this changed. The perception of the word negro now became increasingly negative, and in the late 20th and early 21st centuries, African Americans have instead come to identify with the terms black and African American.