I run a decent amount and I used to be self-conscious about it. Eventually I realized: What does it matter what random strangers think? Their opinion of you has no effect on your life. They won't even know your name or remember your face.

Now it doesn't feel the least bit unusual when I ignore people. I'm breathing hard. In a few minutes I'll be half a mile away from this person. Why spend the effort to make eye contact and nod?