Be all that
Definition 1 of 2
Pro Tip 1/3Cockiness Implication
Using 'be all that' can imply arrogance when someone overestimates their abilities. 
He acts like he's all that at chess, but I've beaten him every time.
Pro Tip 2/3Conversational Tone
The phrase 'be all that' is informal and best used in casual conversations among friends. 
You think you're all that because you won one game?
Pro Tip 3/3Emphasizing Achievement
The phrase can highlight a success but risks sounding boastful if overused. 
After winning the contest, he strutted around like he was all that.