A British professor who specializes in cities and urban life has been convicted of damaging luxury cars with graffiti that was surprisingly polite. Stephen Graham was found guilty yesterday of using a screwdriver to scrawl words such as "very silly," "really wrong" and "arbitrary" into the paintwork of vehicles including a Mercedes, an Audi, and a Volvo. Police pegged the damage at $29,000. The 47-year-old academic previously blamed a bad reaction to alcohol, antibiotics, and prescription drugs for his behavior. He gets sentenced next month.