This achievement is called Intimidator.
Really easy to get all you have to do is Intimidate someone, basically select any dialouge option that would threaten someone, usually has a eye symbol with a lightning bolt in the center of it.
You can get this achievement during the prolouge once you reach the locked gate turn around and go back into the town and head to the left you will see a guard shoot a woman in the back go into the house where the guard was and speak with the two guards and you will have the option to intimidate them.