I don't like it when someone messages me and they start with only "hello" or "hi" without adding anything else. Especially if it's someone I don't know yet. Please give me something more to get the conversation going!
My least favorite is when someone sends a chat message like "Hi, can I ask you a question?" and you just know the reason they didn't come out and say it is because they want to put you on the spot so you're obligated to respond to be polite