To Wave or Not to Wave

When you pass a fellow runner or walker, do you wave, say hello, nod, or just ignore?  When I am out running, I usually just ignore anyone I pass.  While this may seem rude, it really depends on the norms of your community.  In my city, it is not common to acknowledge someone unless you know them.  When my parents visited, they were shocked and thought it was very impolite.  They live in a place where people say hi to one another in passing, whether they know each other or not. 

Of course, there’s an exception to every rule.  A while back, there was a guy I’d see a lot when I went out running.  Every time we passed each other, he held up his hand to give a high five.  That may have been a little much for my parents!

What is your preference?