がつんと言いう

expression, godan verb (-u)

tell someone off emphatically; give someone a piece of one's mind

Used when scolding or reprimanding someone directly and forcefully. The がつんと part is onomatopoeic for a sharp, impactful action.

• 彼かれの失しつ礼れいな態たい度どに、がつんと言いってやった。

  I gave him a piece of my mind for his rude attitude.

• あの上じょう司しは、部ぶ下かがミスをするとすぐがつんと言いう。

  That boss immediately tells off his subordinates when they make a mistake.