Sure, Starkiller had deserved everything he got. Leia had done what he did to her, and with good reason. But, BUT, he was also still an asshole, and not one to let things be. You just didn't have to.
So when the soda was poured in his lap, and Leia left him sitting in the puddle of fizzy drink it boiled in Starkiller's head. Didn't help that he just learned that the Empire was dismantled in it's entirety. By this rebellion? There was no rebellion. There wasn't anything. There was absolutely nothing at all. He was just tasked with finding and building one, to fight against the Empire to help his master take control.
Starkiller left in a huff and followed Leia at a distance at first, but when they drew closer to the area in which he also lived, where Kenobi had shown him, he called out. "Hey." He snarled. "Hey!" He called out a second time. When she turned, the dark side pushed him to choke the life from her corpse, but he curbed that urge.
"What year is it?" Was all he asked. For him it was year sixteen.