I have complained a lot that some drivers won't pass me unless they can give me a RIDICULOUS amount of space. I've had situations where I'm riding on the shoulder, at least a foot right of the white line, in a 14' wide lane, and people wait for traffic to clear and then move BEYOND the oncoming lane and drive in the oncoming SHOULDER to pass me.
When I've had a chance to ask about it, people seem to think that adults riding bikes act the same as 6 year olds riding bikes - they swerve around at random, change direction without looking, commonly wobble about by many feet, and fall every time they hit a pebble in the road. They're "afraid" to pass because they assume that a cyclist is going to suddenly swerve right in front of them at any moment.
I don't have any idea where this comes from. I tell them that I can easily ride down the white line for half a mile without leaving it if I choose to; I ride FAR more straight than I've ever seen any car drive. But they just say "well, that's you. I can't take the chance that someone else won't swerve."
And while I rarely see it, I have occasionally seen the random idiot - last year I saw some moronic teenager who was intentionally weaving back and forth across an entire lane on a 50 MPH road. No traffic in that lane at the time but oncoming drivers would have seen him. So without separated infrastructure I really don't know what to say about these people.
The thing that bugs me about them is that they hold up traffic significantly on 50+ MPH roads, building up lines of 30+ cars behind them, and those people all assume that the backup is because of something I did and are irritated at me.
They're also the kind of people who might think of cyclists as poor addled people who need to be limited "for their own good" and if you tell them that you're a responsible adult, they then think you're being "arrogant."