A/some piece of work
Definition 1 of 3
Pro Tip 1/3Slightly Negative
Suggests negative feelings towards a person or situation without being too harsh. 
He missed another deadline; he's quite a piece of work.
Pro Tip 2/3Sarcastic Tone
Often used with a sarcastic tone to express disbelief or disapproval. 
Left a mess again? You're some piece of work!
Pro Tip 3/3Informal Context
Used in informal conversations among friends or colleagues, not in formal settings. 
Our new neighbor argues about everything; he's a piece of work.