None of us are in your shoes so it's really tough to say what your coworkers' motivations are, but at the end of the day you are yourself, you are in charge of your mental and physical well-being. When someone else does something minor and it affects you strongly it's time to stop thinking about them and start thinking about what's happening in your own body.

Unfortunately your emotions, like being offended, aren't entirely in your control. There are a lot of brain connections rustling around up in your noggin that don't pass through the filter of your consciousness.

The best advice I can offer is to redirect yourself when you start to get offended. Pick a favorite topic, something that you like to think about often, and "switch" to it when you feel yourself getting triggered.

As for how you should act when you aren't greeted directly? I see no reason for you to change your behavior, just act as though nothing happened, because nothing did happen