I know the feeling. I've said hi or waved several times and been ignored. Now, I usually look at an oncoming rider and if they look over at me then I either wave or nod. If they are close enough, I'll say hi. If they won't even look over at me, then I just ignore them. If they say hi first or nod first then I always reply with a wave or a nod and/or smile.
The majority of ppl that ignore you are the lone riders in my experience. For me, I'd say about 25% will wave, say hi, or smile back at you, but I don't keep track really.
Pretty sad state of affairs.
PBW