I agree, it's definitely a form of disrespect and they believe they can get away with it. I really don't say anything especially if it's people much older than me, this is especially true with coworkers. Even though we're on the same level professionally, they're old enough to where they could complain that I was disrespectful even though I wasn't and admin would most likely believe them and not me because I'm 20-30 years younger than my coworkers. Now if it's someone closer to my age and it's not at work, I'm more likely to say something but sometimes that doesn't really help.

There was a time where I said hi to a coworker only for her to tell me she was busy and to leave her alone, seconds later another coworker starts talking to her and they both start talking about what they did over the weekend. Another time a coworker got mad at me for asking a question through text after work, yet she's okay with other people talking to her through text even on group chats. In fact, the latest a coworker texted on group chat was 11pm which is something I wouldn't do since I like to respect other people's boundaries and she had no problem with it. There's been times where she even initiated messages late at night so that's why I don't talk to them unless I absolutely have to, I respect other people's wishes but sometimes people act this way just because they can and there's more examples of this kind of behavior even outside of work.