and how do I react next time they don’t greet me?
I started working at this department 3 weeks ago. I went into the office I now work at, greeted 2 coworkers I’ve already worked with, they looked at me, said nothing, kept talking to themselves.
How am I supposed to interpret that?
To me this is disrespectful, maybe you disagree?
Then, as I was working, I saw both of them staring at me. What am I supposed to do when that happens? To me this signals hostility and passive aggressiveness.
I separate private life from personal one but even I know that the least you can do is to greet your coworkers, unless you want them to quit.
Like others have said, don’t think too much about it. It’s really not that big of a deal to greet your colleagues. If you insist on doing so anyway, do it because you want to, not because you expect something in return.