The most colloquial way to say "give me a break" would be: "me dá um tempo!" It is very very common in Brazilian Portuguese, but it might sound rude... take care.

There is also "Não enche o saco". It is very colloquial but also sounds rather rude when you mean it. I think it is even more common than "me dá um tempo", which sounds a little bit feigned. But beware, it doesn't literally translates to 'give me a break'... it is a slang expression.

I think the way less aggresive is : Um momento, por favor! But you can be cute and gently and say: Só um minutinho!