Said when one is reluctant to make a particular request or accept someone's offer to do something. Often, though, the reluctance is feigned (as to be polite), and one ultimately wants the thing done. A: "I could talk to the boss about it for you." B: "Oh, I couldn't ask you to do that—unless you really want to." It would be great if you could watch the kids for me this afternoon, but I couldn't ask you to do that.