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."