When the player first enters Paradise Falls, they may witness an encounter between Ymir and the bartender Frank. The two begin talking, with Ymir eventually getting angry. He then turns hostile and kills the bartender with his Super Sledge. If the player asks him his reasoning for this, he tells you that the bartender was watering down the drinks so the Slavers would purchase more.
Killing Ymir will leave a finger on his corpse if the player has the Lawbringer Perk. Doing this will cause all of Paradise Falls to become hostile. This will also infuriate his son Jotun who may end up trying to kill everyone in sight.