expression, suru verb (irregular)
act self-importantly; be arrogant; throw one's weight around
Colloquial expression; literally 'make a big face', used for someone acting superior or overbearing. Often implies a temporary attitude rather than a permanent trait.
See also: 大きな顔をする
Ever since he got promoted, he's been acting all high and mighty, hasn't he?
あいつ、先輩の前ででかい顔するなよ。
Don't go acting all self-important in front of the senior members.