You silly ass, dirty Indian... I said hello.

This is a tricky subject for me, because I have something of a social anxiety issue. So whenever I see that I'm about to pass by another person, I start thinking to myself, trying to decide what would be the most appropriate thing to do. However, my mind's defense mechanism against other humans immediately starts coming up with plans of action in case that person decides to attack, heckle, or become aggressive in some way. This makes me nervous, and I usually decide the best thing I can do is to pretend I'm so caught up in my business (remembering a shopping list or some bullshit) that I don't even notice them. Because I'm so neurotic though, I keep checking to see if the other person is smiling, nodding, or looking like they might say "Hi". I do want to respond if that happens, of course; I'm a nice guy. But since I'm trying to pretend not to notice them at the same time as I'm anticipating and preparing for possible interaction, I probably look like I'm being rude. Sometimes I think that other people think I'm blatantly snubbing them, as if I want them to know that I'm too cool to deign myself to greet them.

If someone actually does say "Hi" or nods to me, I'll usually intend to say "Hi" back, but mostly all I manage is a "Hey" under my breath or a sort of half-smile. I probably creep most people out.

So yeah, if someone acts crazy like that when you greet them, you shouldn't assume that they're a dick. They might just be neurotic and/or have self-esteem issues.

Also, I'll cosign what everyone said about cultural differences. In some parts of the world it's considered a sign of respect to not make eye contact.

Jam it back in, in the dark.