Derek was always careful to follow the rules of the road when he drove. The fact that he occasionally carted around bodies and out of control werewolves meant he liked to fly under the radar of the Sheriff's department as much as possible, even though Stilinski knew the truth and would help cover things up as much as he could. There were always douchebags like McCall's father wanting to come in and swing their dicks around about the number of 'unsolved' cases in Beacon Hills.
When he realized who pulled him over, he couldn't help but chuckle. Apparently it was going to be one of those kind of nights. Meeting Karrin had been unexpected, but in the best possible way. After his failed relationships with Kate and Jennifer, he hadn't been looking for anything more than a little fun, but she somehow managed to worm her way into his heart.
They were keeping quiet about their relationship for the time being. The last thing Derek wanted was a bunch of teenagers or Stilinski sticking their nose into his private business. Plus the secrecy made it hotter.
He rolled down the window and flashed a charming grin. "Officer, what did I do wrong?" he asked.