Only when he stops breathing - Deadpool

Set the Dialogue Volume Slider to zero - 10

This is a super easy achievement. Before the game has probably started, before you talk control of Deadpool. Go into the Main Menu, then into Audio Options. Dialogue is the bottom slider. Slide it all the way to zero. This will make no noises be heard, even Deadpool's.

This is a reference because Deadpool is infamous for always having something to say, never being able to shut up.

Deadpool