Just a quick note from someone who doesn't post here: I'm Brazilian and I have absolutely no problem with any of our neighbours. In fact, I think Argentina and Portugal are great countries (just to name a few of which some people claim to be hated by Brazilians).
I live too far from Rio so probably won't be at any of the ceremonies but I'd be very more than happy to cheer for any athlete, from any country, from any continent, of any religion, of any sexual orientation and so on. Unfortunately, I can't guarantee others will behave in a mature way. I find it appalling, ridiculous and very childish that some Brazilians love to create problems where there is none with regard to these silly rivalries. The problem may be that the "childish" minority can be very noisy. I don't know people from SaoPaulo who hate Rio with all their might, neither the reciprocal situation, but we hear -more frequently than one woul like to- about these claims in this very forum.
I expected the Brazilian government or the sports committees to try to explain the population about the importance of being good (respectful, warm, kind, etc) hosts but I don't think it's going to happen. All I can hope for is that these people grow up by then, including some of our colleagues here.