I was riding home late one night on a bike path here in Boston and had a similar incident.

It was about 12:30 am and I was in a particularly creepy quiet part of the path and fuming about what a jerk the director I was working with was when a guy stepped out of the bushes in full camouflage gear. Fortunately, I had simultaneously vocalized a particularly vicious string of expletives at full volume and it absolutely scared the crap out of the guy. I had no time to react to the Rambo-man and am ever thankful to the tyrant of a director I was working with at the time- "Hail, effing Caesar!"

My advice: render unto Caesar what is due Caesar- a face full of mace or an earful of expletives.