"There actually aren't that many people running out on the Charles so you don't pass people with that much frequency. But.. almost NO ONE gives any sign of acknowledgement, no nod, nothing."
There aren't many people running along ("out on" would be a neat trick) the Charles? Wha? I went to law school in Boston, travel there monthly for business, and have run along the Charles hundreds of times. Typically I'll see a hundred other runners. It'd be bizarre to wave or nod to dozens of other people who are doing the same thing that you are.
Maybe you're thinking of some other river. Or maybe you're making this shit up.