This one makes me laugh, because it's totally true. I've noticed that, the further out on the backroads you travel, the more likely you are to see total strangers waving at you as you pass by. I'm not sure why that is; maybe we're just so darn excited to encounter another human being where the traffic is so sparse.
I imagine it looks funny to outsiders, though:
"Who was that?"
I don't know.
"Then why did you wave at him?"
Because he waved at me.
"Why did he wave at you?"
How am I supposed to know?