From Longman Dictionary of Contemporary Englishlook who’s talking, look who’s talkinglook who’s talking, (also you’re a fine one to talk, you can talk) spokenCRITICIZE used to tell someone they should not criticize someone else’s behaviour because their own behaviour is just as bad ‘Peggy shouldn’t smoke so much.’ ‘Look who’s talking!’ → talk
Examples from the Corpus
look who’s talking, • "You need to get more exercise." "Look who's talking!" 