You get up from the sofa. Before you’ve even reached the kitchen, someone says:
Já que você tá de pé, pega um copo d’água pra mim?
Since you’re up, could you get me a glass of water?
All you did was stand up. Now you’re taking orders.
There’s a neat little piece of language at work here. Já que introduces something the speaker treats as already established, then uses it to justify what comes next. You’re already up, so getting that glass of water is presented as an easy addition to whatever you were doing.
The same pattern works beyond the sofa. Já que você vai ao mercado, traz pão? means “Since you’re going to the supermarket, could you bring some bread?” The trip was your idea. The bread was someone else’s.
And a request can collect another request: Aproveita e pega um pra mim também. While you’re at it, get one for me too. One person gets up; three people are suddenly thirsty.
What phrase in Brazilian Portuguese tells you a favour is coming before anyone actually asks? Who says it, and what usually comes next?