冗談はやめて。

冗談はやめて。

Get serious.

冗談(じょうだん)はやめて。

Jōdan wa yamete.

冗談 (じょうだん、ぎだん、げだん)

jest; joke; funny story

は (は)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

止める (やめる)

to stop (an activity); to cease; to discontinue; to end; to quit; to cancel; to abandon; to give up; to abolish; to abstain; to refrain

Reading: ジョウ

Meanings: superfluous, uselessness

Reading: ダン

Meanings: discuss, talk