What's the dumbest thing you've seen a traveler do?

We've seen it all on the roads and rails of Washington: people putting on makeup in their cars; folks shaving on the Metro; drivers making left turns from far right lanes. What behavior have you seen that left you gaping in amazement? What are the offenses you see your fellow drivers and transit riders commit every day? Share them in Dr. Gridlock's discussion forum Taken for a Ride.