Some runners seem to find it just too too difficult. It's not so bad when they're coming towards you; you can see the effort being made and I tend to make allowances. A grimace, an eyebrow raise, even a faint twitch will do.
But it does hack me off a bit when they overtake me, I say a cheery-ish Good Morning and get naff-all in return. Some great hulk thudded past me this morning without so much as a by-your-leave. Passers by were treated to my Good Morning, Good Morning? The best to you each Morning?? routine, and then several iterations of two fingers waved at unresponsive hulk's departing back.
Really, is it so hard to manage a bit of basic politeness?
Oh, and I ran for 1 hour, 5 mins and did 10.3K. Yay!! Good morning!!!!