that's a good one

Interjection

informal

(informal) That's a funny joke (often said to indicate that what has just been said is laughably unbelievable.)

Japanese Meaning

面白い冗談、笑いを誘うほど信じがたいジョーク / 聞いた直後に面白さを感じる冗談

When he said he could finish the book in a day, that's a good one.

彼が一日で本を読み終えられると言ったとき、そんなの冗談だよ。

Sense（1）

(informal) That's a funny joke (often said to indicate that what has just been said is laughably unbelievable.)