The interactive psychology between bicyclists and drivers is very interesting to me and I hope someone does a serious and comprehensive study of the issue someday. The results should be most interesting.

Many drivers are not bothered at all by cyclists.
Many are nearly driven around the bend at the mere sight of a bicyclist.
My hunch is that on a basic level seeing someone choosing to transport themselves on a small, inexpensive, vulnerable bicycle upsets major parameters within which most individuals build their self image and therefore structure their lives.
Most drivers buy into the notions, that are well exploited by automobile marketers, that they are better off people (and maybe better people) if they have new, shiny, safer, more powerful means of individual transport that they develop a view of as an extension of themselves.
The costs involved, both financially and otherwise, in maintaining this structure then tends to dominate and re-order many other aspects of peoples lives.
Enter someone who has simply chosen to bypass all of this and actually seems to actually be enjoying it. This makes people feel frustration on some level which is often expressed by engine revving or some other assertive gesture.
All of this is aggravated if the individual feels incapable of exploiting the bicycle option themselves for physical or social reasons.

Yes, I have spent way to much time pondering driver attitudes.