expression
not one to talk; look who's talking
Used to point out hypocrisy: the speaker is in no position to criticize others because they have the same fault. Often follows a statement about someone else's flaw.
See also: 人のことを言う (ひとのことをいう)
彼は遅刻が多いけど、私も人のこと言えない。
He's often late, but I'm not one to talk.
「またミスしたの？」「人のこと言えないでしょ。」
"You made another mistake?" "Look who's talking."
The affirmative form meaning 'to talk about others'; 人のこと言えない is its negative potential form used idiomatically.
From 人のことを言えない, literally 'cannot say about others', used idiomatically to mean one is in no position to criticize.