I pretty much say hello to everyone....certainly no discrimination based on how fast or slow someone is. I say hello to people with headphones cause usually I don't realize they have headphones on until it is too late....I figure they at least saw my lips moving and sometimes they smile at me.
I certainly say hello and give respect to people who clearly are NOT runners and are out trying to get in shape or lose weight. I feel some camaraderie with them cause at least they might have some dedication to it. Hopefully.
Sometimes when I do say hello it doesn't really come out (like my voice doesn't work well, cause I might not have spoken in over an hour) and always feel dumb then....sometimes I think other people might think I just snubbed them, but really it was just that my voice is broken). So if you see me and that happens, please understand.
What do you guys do when you see someone ahead on a trail that not many people are on (or it is late at night). If they are going the same direction as me (i.e. I am coming up behind them) I cough fairly loudly when I'm still like 30 meters back and usually they hear and turn around to see who is there. Then I look down really quickly like I didn't cough for that reason. I scared two girls on a path in Rock Creek Park (notorious for people finding dead bodies there) near where I live by coming up behind them after dark. I didn't see them until I was almost on top of them because they were around a bend in the path. So now I always cough or something.
I actually usually don't say hello to people running really fast (all you saying you are going sub 6:00 or under).....cause I figure they don't want to be bothered. I certainly don't want people saying hello in the middle of my interval workouts.