I'm so glad this thread was made. Listen to what happened to me on this past Saturday morning: I came into town for the long labor day weekend and met up with an old running buddy for a long run. As we were finishing up, we were going over this bridge and were about to pass this older guy (40-45yrs old?) and he sped up a little. We were cruising pretty good, so we got by him pretty easily, but then he sped up even more and stayed a rude 5 meters behind us for a while. It was really weird and my friend and I both got a little worried this was some weirdo that was capable of anything. We sped up a little to get rid of this creep and sure enough he came picked it up with us. We took a left after we crossed the bridge and he took one too. Once we got back to our cars, my friend called it a day at 18 miles and I decided to add on another couple easy miles to hit 20. I took another left to head towards a nice plush trail that goes around an island in the middle of the city and sure enough this old man follows me. At that point, I basically come to a stop and let him pass because I don't want to go on to this less populated island with some weirdo following me. He passes me and I make a couple remarks to let him know what he did was not cool and he starts shouting his PRs at me, which were probably from 20 years ago. His PRs were pretty good and he's not some hobby jogger, but on this day he definitely acted like one. I continued onto the island, he took a right, I made a left, saw that he was out of view and then got the hell out of there and added on somewhere else.