Social media can be like alcohol. It releases inhibitions. People tend to do things that they wouldn't do in real life ...
Also, many users see it primarily as a marketing tool. They're often not remotely interested in interaction. They just want you to buy their stuff and that's it. Ironically, if they did embrace the interaction they would make more sales.
Because of these influences you get a lot of behaviour that is actually anti-social. That can be quite depressing given the context.
Automated direct messages
A lot of people absolutely detest these! As long as they're just a thank you they don't usually bother me. It's when they immediately start trying to get you to sign up to something, or flog their products or services that my temperature goes up.
Sometimes they'll ask you for something, too, such as likes, etc. Don't like that all. It's the pushiness that really puts me off.
That can apply to any other kind of interaction on Twitter, Facebook, and similar sites. I just recoil when all you get from someone is an overt attempt to sell or promote.
Another pet peeve is when someone you've just connected with on Twitter asks you a question like "How are you?" as if they want to actually start a conversation. Then you look at their stream and see they're doing exactly the same thing with everyone. They've probably even got some software to do it.
I find that even more irksome because they clearly know engagement is key, but they're not doing it in a genuine way. So it's calculating as well as insincere.
I think the key element I find off-putting is selfishness -- people using these platforms to just say gimme, gimme, gimme! These are often minor things but they do accumulate and you end up with a lower threshold of tolerance for them.
Recently, for example, some guy liked a comment I made in a Linkedin group discussion that referred to a post from his blog. So he sent me a message asking me to write the very same comment on the blog to beef up the interaction!
Another practice that gets my goat is when people go overboard with the cross promotion. They tweet you to a Google Plus update ... which sends you to a Tumblr post ... that points you to a Facebook page update ... that finally links to their blog post! Why not just send people to the post directly?
I know they're just trying to get their other profiles known. But doing it this way just wastes people's time and effort.
I know I'm starting to sound like a bit of a grouch. But there are still more things that peeve me. Private Twitter accounts, for example. I often follow people back but not if they've got that little padlock icon. It seems petty and even a tad paranoid to me. If you were a whistleblower or a citizen journalist in some totalitarian country, sure. But not if you're just tweeting about stuff generally. Why such an intense need for control?
Another biggie -- and one that I'm sure many people can relate to -- is being added to Facebook groups without your consent, often by people you've had little or no interaction with aside from the initial connection.
Still on Facebook: I don't like it when people repeatedly suggest that I connect with their friends. Not so bad if I share an interest. But for personal, friendly connections it can get a bit OTT after a while. I feel like saying to them: Don't you get it? I'm not interested!
Another thing that annoys me on Facebook is when people like my page, then immediately say in a comment (or worse still, in a message) that they want me to like theirs. After a while, that gets a bit tiresome even when they're in the same niche as me. And if their page has nothing in common with mine, and I'm not interested in what theirs is about, that annoys me.
Basically, I won't like a page unless I'm interested in it. And I don't expect the owner to like mine back -- although of course it's always nice when that happens. But being demanding is just rude.
I suppose that people do this because it does work for them and their numbers improve. But apart from the fact that this is pushy, it's always better to focus on quality over quantity (both in terms of content shared and the nature of the following itself).
When it comes to these etiquette issues I think a good rule of thumb is that if you'd feel uncomfortable approaching people in a certain way in real life then don't do it on a social network!