I only had 2 incidents where I felt a bit at risk. Both were from guys in cars. I had stopped for a quick break and they pulled just a little bit too close and looked a bit too interested in me or, more likely, my possessions. Each time I took out my cell phone, fake dialed and then had a wild and loud conversation with myself, making sure to describe my surroundings and the fact that someone else was there. I pointed, waved my arms around, etc. The first time, I just hopped on my bike. The second time, the guy spun out of the park where I was sitting and I never saw hide nor hair of him again.
Gotta love technology!
BTW, most times, people were more than kind. As soon as they see you, they like to talk, ask questions, offer you a coffee/cold drink/sandwich, etc. Itīs actually a wonderful way to meet people.