If it expresses the superiority or inferiority of one race over another. Plain and simple.
The hard part is justifying whether or not a viewpoint meets this criteria.
What do you think of comments like Obama asking 'blacks to activate' for Hillary? Is that racist? I think in a sense it is a stereotyped view of African Americans as bloc voters for Democrats. Almost like the modern, watered-down version of what LBJ discussed in the mid-60's with his Great Society.
Obviously any one that were to ask for whites or even say Bosnians and Ukrainians to vote for X candidate based on their ethnic or racial origins in a block is a person to be concerned with.
What do you feel about African-Americans who purposefully call out white liberals as dangerous - like Malcolm X or Farrakhan (on their own and apart from other attacks on other ethnic groups)?
I really disdain collectivist, assumptive views like blacks calling other blacks who decide to be Greens, Sanders supporters, Libertarians, or Republicans as 'race traitors', 'oreos' or 'Uncle Tom's'.
For instance also if someone does not like Ted Cruz or Marco Rubio then why do some people including Latinos feel the need to drop a phrase like 'coconut' why not just pile on that person. They should be bad enough on their own record without the ethnic mention if you are so against them. It's like saying - "No, you're so bad you are no longer able to call yourself Cuban-American".
Overall, it is a very base, tribal view of people and does not speak highly of who says it.