A former bus driver has pleaded guilty to backhanding a 21-year-old passenger with Down syndrome because he was irritated by his attempt to start a conversation. John Marrs of Beverly pleaded guilty Wednesday in Salem District Court to a charge of assault and battery on a disabled person. The Salem News reported that Marrs, 53, was sentenced to a year of probation and was ordered to take anger management classes and barred from working with the disabled. Marrs was a driver for Danvers-based LBK Transportation, which provides rides for developmentally and intellectually disabled people, at the time of the September 2012 assault. He has since been fired.