Also found in: Wikipedia.
1. Inf. You are not kidding me, are you? (An expression of mild surprise.) Jane: I got elected vice president. Bill: No kidding! That's great!
2. Inf. Everyone already knows that! Did you just find that out? (Sarcastic.) Sue: It looks like taxes will be increasing. Tom: No kidding! What do you expect? Alice: I'm afraid I'm putting on a little weight. Jane: No kidding!
exclam. I am not kidding.; You are not kidding (are you)? No kidding! I never thought she would do that.