かっこつける

ichidan verb, intransitive verb

show off; try to look cool; put on airs

Casual, often mildly critical; used when someone is trying too hard to appear stylish or impressive.

• 彼かれはいつもかっこつけて話はなす。

  He always talks trying to sound cool.

• そんなにかっこつけなくてもいいよ。

  You don't have to try so hard to look cool.