Like me, you might have assumed it means "OK". Because that's what it has meant your entire life. It doesn't. It doesn't mean that at all.
Actually, here, it means something worse than "asshole". And somebody finally told me what I've been flashing around at them for eight days. And as you can imagine, since I am walking around in a country where I CAN'T COMMUNICATE WITH ANYBODY, I've been flashing it plenty. I guess I like to let people know I'm "OK". Think about all the times you might use it, especially if you didn't speak the language, for example: 'This food is great', 'I can see just fine from here', 'I got a photo', 'thanks for the beer', 'I understand', etc, etc, etc.
SO. Here's how to really say, "OK" in Brazil. You simply turn your asshole on it's side, OK?
Or, just go with another old favorite. (I wonder what this one really means?)