Inspired by a popular guide to Understanding the British, I've put together a few entries in a Foreigners' Guide to Understanding Brazilians. Portuguese speakers and Brazilianists are invited to add more in the comments. Hat tip to Brazil-based journalists Andrew Downie andDom Phillips, who contributed items, and Olivier Teboul, a Frenchman living in Belo Horizonte whose list of "Brazilian curiosities" (in Portuguese) has generated a huge response from amused, and sometimes bemused, locals. 
What Brazilians say: Yes (Sim)
What foreigners hear: Yes
What Brazilians mean: Anything from yes through perhaps to no
What Brazilians say: Perhaps (Talvez)
What foreigners hear: Perhaps
What Brazilians mean: No
What Brazilians say: No (Não)
What foreigners hear (on the very rare occasion a Brazilian says it): No
What Brazilians mean: Absolutely never, not in a million years, this is the craziest thing I've ever been asked
What Brazilians say: I'm nearly there (Tô chegando)
What foreigners hear: He's nearly here
What Brazilians mean: I've set out
What Brazilians say: I'll be there in ten minutes (Vou chegar em dez minutinhos)
What foreigners hear: He'll be here soon
What Brazilians mean: Some time in the next half-hour I'll get up off the sofa and start looking for my car keys
What Brazilians say: I'll show up later (Vou aparecer mais tarde)
What foreigners hear: He'll be here later
What Brazilians mean: I won't be coming
What Brazilians say: Let's stay in touch, ok? (A gente se vê, vamos combinar, ta?)
What foreigners hear: He'd like to stay in touch (though, puzzlingly, we don't seem to have swapped contact details)
What Brazilians mean: No more than a Briton means by: "Nice weather, isn't it?"
What Brazilians say: I'm going to tell you something/ Let me tell you something/ It's the following/ Just look and you'll see (Vou te falar uma coisa/ Deixa te falar uma coisa/ É o seguinte/ Olha só pra você ver)
What foreigners hear (especially after many repetitions): He thinks I'm totally inattentive or perhaps mentally deficient
What Brazilians mean: Ahem (it's just a verbal throat-clear)
What Brazilians say:  A hug! A kiss!  (Um abraço! Um beijo!)
What foreigners hear: I've clearly made quite an impression—we've just met but he/she really likes me!
Waht Brazilians mean: Take care, cheers, bye
What Brazilians say: You speak Portuguese really, really well! (Você fala português super-bem!)
What foreigners hear: How great! My grammar and accent must be coming on a lot better than I thought
What Brazilians mean: How great! A foreigner is trying to learn Portuguese! Admittedly, the grammar and accent are so awful I can barely understand a word... but anyway! A foreigner is trying to learn Portuguese!