This guy was definitely a psychopath. Everyone here must have been, and in the second Stu was left directionless without a proper leader, kneeling on the floor as the aliens around him scrambled, he could feel the fear in his belly that only Billy had ever caused before, suddenly so aware of how alone he was surrounded by people who didn't care about anything. He barked a laugh as Donnie stared back at him so coldly like he didn't even recognize a human, loud and short, because Stu had no where else for that anxiety to go. Not until he realized that he was being left behind and not following the crew, and he had to quickly scramble to his feet to catch the ladder after them so they didn't forget him.