A response when someone tells you to try something and you don't really want to. Can also be used as: I'll take your word for that.
Boy: "You should try these clams. They're really good."
Girl: "I'll take your word for it."
A negative statement to describe a situation.
Girl A: "You put the Jacob fans and the Edward fans of Twilight in the same room?"
Girl B: "Yes."
Girl A: "This won't end well."
A statement used to agree with another statement or plan. Different adjectives can be used in place of vague:
Boy A: "So we'll knock on the door."
Boy B: "And then?
Boy A: "Then we'll do something else."
Boy B: "Wow that's just vague enough to work."