SOmetimes my strategy is to try to convey that I'm a wilder card than they are - or at least that the don't bother me. THat's weird enough behavior that it's safe to say he was at best seeing how you'd respond (for his amusement at your discomfort)... so I wouldn't give hmi the satisfaction of discomfort, but get something that at least *looks* like a camera and have it handy - or a digital recorder or a cell phone to ever so confidently speak into.
In town I have been known to ride up closely to the back of a car at the light - just being "assertive," and maybe get 'em wondering what I'm doing with my Sharpie pen back there (the one I carry around to correct any grammar errors I may find :-)). It's only when it's fairly busy, though - and it's never so busy that somebody could be inconspicuous.
I'd probably also let my pepper spray dangle more visibly from my fanny pack. (Hey, no dogs have even approached me since I started carrying it - it works!)
... and if there were another route, I'd take it...