smile when you say that
You had better be joking, or else I am going to get really angry, upset, or offended. A: "We got it done eventually, no thanks to this lazy good-for-nothing." B: "Smile when you say that! I'm standing right here, for Pete's sake!"
smile when you say that
Inf. I will interpret that remark as a joke or as kidding. John: You're a real pain in the neck. Bob: Smile when you say that. Sue: I'm going to bop you on the head! John: Smile when you say that!
Smile when you say that
sent. Give some sort of a signal that you are only joking when you say something potentially offensive. I told him he’d better smile when he says that, or he’s going to get in trouble.