Stiles was talking to Scott, he had planned on telling him everything, everything about how he accidentally killed Donovan in self defense, little did he knew, Theo had already gave Scott the story, making it sound like Stiles killed Donovan out of pure rage and madness. Stiles is baffled by how Scott handled the story He was trying to explain that he couldn't protect himself in any other way and he's not an alpha werewolf like Scott he's just a human, but Scott not knowing the exact manner of the event told him that we don't kill people. So with an argument like that thanks to Theo they took different paths, Stiles was furious. He got in to his car and drove away only for his jeep to broke down on him. He got out trying to fix the car it was raining, his eyes met with the missing spanner a reminder of what happened with Donovan and Scott not believing him. He grabbed the spanner Taking a step forward to throw it in to the woods but changed his mind and threw it towards his jeep instead. The spanner hit the windshield and broke the glass. He got down next to his car sitting down with his back pressed to the tire of his car feeling devastated