Look who’s talking
Definition 1 of 1
Pro Tip 1/3Irony Usage
The phrase can be used ironically to point out someone's lack of self-awareness. 
When the messy roommate complained about a few dishes, I had to say, 'Look who's talking!'
Pro Tip 2/3Casual Tone
It's normally used in informal contexts among friends or family, not in professional settings. 
After my sister criticized my TV choices, I laughed and said, 'Look who's talking!'
Pro Tip 3/3Deflecting Criticism
This phrase is used to deflect criticism by highlighting the critic's own flaws. 
My boyfriend told me I spend too much time on my phone, so I replied, 'Look who's talking!'