I don't mind a "Hi." followed by some [user is typing] followed by the actual question. It's the naked "hi" with nothing else. The "hi" that's just dropped there awaiting me to confirm that I'm now a part of a conversation I know nothing about.
Emails have subject lines and require the sender to write out what they want. Phone calls leave me the option to pick up or let go to VM if I'm not available. But DMs are the worst of those two: text like an email, realtime like a phone call.
For some reason those seem to correlate with users who want me to do their work for them, or are about to drop a request that I have no time for—and don't even have the time to explain why it's not my domain or a good fit for my schedule. These are requests I'd love to get via email so I can respond on my own time. Or as a voicemail. Or even as a written out DM.
But not as another message in "a conversation we're having now."
Was it a nuisance when work from home started more and more people switched over to this pattern.
Nowadays I am just fed up with it.
But it might be because after 23 months we (the company I am working for) still haven't been able to learn how to replace most meetings with forms that don't take up that much synchronous time.
Most meetings I am in could be at least cut short when prepared up front by a document that enables commenting. Then one could discuss ideas and not need to generate them on the fly.
And then there are the few cases where the need is to brainstorm. These can be fun. And I like them. But they are for cases when the map/way/ideas are yet unknown.
When the path is more clear things imho should be more asynchronously organized.
On IRC this is called "scrolling" and depending on your relationship with the person you can ask them if someone is playing a joke by hooking their enter key up to their spacebar.
In general I think what's happening is a tell that a person doesn't act with fully-formed thoughts when they open their mouth.
I pretty much agree with the other comments against people just saying 'hi' and nothing else. But this made it click to me.
I think many of the people who do this are the same who drop by your desk and ask for a random thing, without taking the time to ask whether you're available or not. This is the same thing, just moved online.
Also, bonus points for people who just say 'hi', you say hi back, and they never reply anything. Reminds me of people in person who would come up to your desk, say hi, while at the same time frantically typing on their phones and making you wait.
I completely understand where you are coming from. But rest assured, your politeness is stressing the people around you and lack of it will at worst perceived as rushness.
I like to be friendly but also to not to waste time by doing some kind of weird manual slack handshake protocol.