There just aren't as many rules for us to break as there are for cars. Running a stop sign is probably the most common, but in some jurisdictions that's now legal. Rolling through a red light is another, and again, in some areas that's legal. I'd hazard to guess that rolling through a stop sign and speeding are by far the most common motorist offence, but also illegal lane changes and illegal turns. Ultimately, though, distracted driving may eclipse all of these, and pose the most danger to cyclists.