Motorcyclists around here behave themselves pretty well, but it's probably because pick-up drivers run them over if they don't.
We have a big problem in my neighborhood, specifically, with bicyclists who don't obey traffic signs. I've very nearly run over several kids because they completely ignore stop signs, etc. Luckily, the speed limit is 20 so I'm never going so fast I can't stop, but it damn near gives me a heart attack.
There's a guy who drives a cable TV truck that I often find myself following on my way to work. He invariably drives 10 mph UNDER the speed limit and then runs red lights. I just don't understand.
I've also got issues with people driving more car than they can handle. I thought it was just because I was a tree-hugging, economy-car driving, liberal until I nearly got run over in a parking lot by a woman in a GMC Yukon Denali because she couldn't back it up. Lady, if you can't steer it, get something smaller.