Honking when they're passing me in the rightmost lane, exactly AS they pass (i.e. after it's too late for it to serve as any kind of warning to me not to swerve to the left), is an act I have trouble interpreting in any way other than, "Hey, let's see if we can scare that dork on the bicycle."
However, today, rather than cursing and being in a pissed-off frame of mind for the next mile whenever this happened, I tried just taking a deep breath, as stress management experts always recommend.
It actually works :)
Of course, since I don't REALLY know what the drivers are trying to accomplish by honking, in theory I could just interpret the honks in some other way: after all, as the stoic philosopher Epictetus once pointed out, "Men are disturbed not by the things that happen, but by their opinions of the things that happen." Unfortunately, though, that's one theory which I've never been enlightened enough to reliably put into practice :)