"Give me a break"

I don't know when to use that expression.

It can be used wherever most expressions of incredulity are appropriate.

"Hey, did you hear about that war in Iraq?"

"Yes. What about it?"

"I hear those Americans are planning on building a permanent Halliburton regional office in order to control the Iraqi oil reserves."

"You're being paranoid. I'm sure that they only want to secure the oil reserves so that the Iraqis themselves can manage them."

"Oh, give me a break. I bet you voted for Blair."

thnx David, but I had another question: now that you mentioned an idea that strongly agree with, is there any expression that I could use to explain myself. Kinda opposite to " gimme a break".

You bet!