If I say I don't want to live in certain parts of Chelsea, East Boston, or Roxbury because it's a S***hole, does that make me a racist?
I don't think it makes you a racist. And BTW Trump's comment (in and of itself) probably does not make him racist. Those who call him racist are generally looking at a pattern of racially charged/insensitive remarks. I don't believe Trump is a true racist (ie, one who uses power to consciously discriminate or oppress based on a person's race). I think he is impulsive and jumps quickly at times to stereotypic conclusions. Thus, he gives fuel to the fire to those who consider him racist.
That said, there are a few important distinctions that make your hypothetical comment different contextually than Trump's comment. The most important being, simply, he is the POTUS and you are a Cblog poster (not to diminish the importance of that). The things that he says are reflective of the country and he needs to be sensitive to American citizens and those around the world who come from these "s-holes" and yet are productive citizens. 2nd, his statement disparages predominantly black/brown countries while essentially praising a fairly homogenously white country. I admit it's "optics" to some extent in that, indeed, the specific country he refers to (Haiti) and some of the countries he included among African nations are generally poor. But it negates the reality that good, smart, productive and in some cases, quite desperate people seek a better life in America regardless of country of origin. Probably better to show some sensitivity to people who live under difficult conditions and perhaps view America as a place where some people from those countries have thrived and contributed.
My guess is that when you call Roxbury, East Boston or Chelsea S-holes and by implication you disparage (in the Trump metaphor -- "we don't want you here") those who live there -- my guess is that even those town inhabitants or observers that understand your characterization might be very displeased with the blanket negativity of it.