Meaning of 真顔がもう冗談


> 「僕はあまり冗談は言わないよ」
>
> 「あっはー。その **真顔が、もう冗談** だよね」

Based on context I assume he said the first line with a serious face (based on
her reply), but I'm not quite sure how to interpret what she means by his
straight face / serious look being a joke.




It's hard to say without more context but I'd guess either of the following:
a.) There is something hilarious he had said previously with his straight
face, making it even more hilarious. b.) The fact that he always has a
straight face is ridiculous. (Could be said in a mean way, like "I'm not
joking" "Yeah? Well, your face is a joke!!")

