It's quite strange, but some people seem to get upset at the sheer speed of a bike. No matter how wide a berth you give them, no matter how early they see you coming, no matter that you slow down the second you see them and maybe pass them at a joggers pace - the fact that you at some point were moving a lot faster than they were truly upsets/provokes/frightens some people. And if you happen to wearing tightfitting lycra you're pretty much the devil incarnate.

I see it all the time on this one gravel road I ride in the woods. It's HUGE and completely straight, you could drive a logging truck down the one side and nary bother the walkers on the other side, but bike riders riding at an average training pace still get black looks from a certain segment of those walkers. As they pass with 10 feet to spare.