Said when someone is overly proud (and the speaker thinks that he should be more humble). Literally, “to make one's face large.” Having a large face means people are more likely to take notice of you.
kare wa mada shin nyuu sha in na noni, mou ookina kao wo shiteiru.
Although he's still a new employee, he sure acts like a big shot.
まだ mada—still (only a new employee)
新入社員 shin nyuu sha in—new employee
[lit: 新 shin (new); 入 nyuu (enter); 社 sha (company); 員 in (member)]
なのに nanoni—although; in spite of the fact...