Two have always jumped out at me. Both lines are from the original "Godfather" with the first being between Michael and Carlo when he comes with his goons and he says, "You have to answer for Santino, Carlo." Just the way Pacino delivered the line, you knew it was going to end badly.

The second would be between Tom and Sal...

"Can you get me off the hook, Tom? For old times sake?"
"Can't do it, Sally."

I love it!!