The issue that I've had is drivers of diesel pickup trucks. It seems that most of these nitwits have gotten a memo that says it's really cool to pass a cyclist very slowly and floor it when they are next to the cyclist and engulf them in dark/black exhaust. It happened to me three times in one 25 mile ride recently.

A BNSF Railroad truck passed me VERY CLOSELY in a 30mph zone and floored it so that the right exiting exhaust (about 2' off the ground) would make a direct hit on me. I was riding right on top of the white line and he had plenty of room to pass safely, without nearly sideswiping me and blasting me with noise and exhaust!

It seems like I can go weeks without an unpleasant incident and then I get a bunch of them very close together. I would love to see some of these fools ticketed for their antics.