They make it all about them. You can recognize these “friends” by the way they consistently make the First Comment, and it’s usually only tangentially related to what you wrote (but always about them!) They crave exposure and love that you have a big online audience. Do not feel bad about telling them to take a hike — people like this make online communities lame.
You have incompatible senses of humor. A long time ago, a friend sent me a pornographic image of Maggie Simpson. Besides probably being illegal, I found it disgusting and offensive and gave the friend a piece of my mind. He called me a prude. Could this friendship be saved? No, it couldn’t. Life went on.
The flip side of this is that if you enjoy snarky humor and someone in your audience can’t roll with that — do them a favor and be very clear that this is who you are, you’re not going to change, and they are welcome to leave if they don’t like it.
Your friend is a trainwreck. Always sick, never can pay the bills, everyone is mean to her, her job gets worse every day… Listen, if all your friend wants is sympathy and {{{hugs}}}, what’s in it for you? Surely you’re not a Messiah who can fix people. We all go through horrible times, sometimes for months — but if your friend shows no other side than Tragic Victim, move on.
Your “friend” turns out to be a professional friend collector. Ever add someone, only to find that they have 1,000 friends and most of their updates involve selling something? Yeah, get rid of those people.
You probably shouldn’t have become “friends” in the first place. You talk to a nice person at Meetup. Immediately, she adds you as a Facebook friend. You quickly find out that she strongly dislikes your religion or political background. You can spend the next several years being a model example of a Tolerant Evangelical Christian or a Common Sense Liberal to keep her liking you, but chances are you’re probably just going to get frustrated and end up filtering each other out before finally one of you makes the purge (“It’s not you, it’s me…”). Be careful who you add.
You find their interactions to be tiring rather than enjoyable. Your friend is nice. Occasionally witty. Beyond that, something is missing — but the bad news is that your friend doesn’t realize it, and wants to talk to you all the time. About nothing.
Make yourself scarce, and don’t apologize for it. You’re allowed.
When you should NOT break up with an online friend
One of you goes through a major life change. Your friend has a baby and can no longer devote a lot of time toward helping you debate feminism with high school students. She soon starts writing about the baby every day. You can either blow her off because she no longer serves your needs, which I think is selfish and lame, or you can appreciate her side of the fence (while she can look over and appreciate yours.) Remember the reasons why you became friends.
They experience a crisis. I can’t believe I have to write this, but if a friend loses a loved one, let him grieve. Endlessly. You are not obligated to comment on every update. Just be there. Grief is not selfish. Don’t ditch a friend who is down.
You get into a fight. I can’t count on two hands how many of my dearest friends started out as enemies. Debate is good for you. Fighting can be a normal part of friendships, as long as it’s not over a deal-breaker (like inappropriate Maggie Simpson pictures). Evaluate whether your argument is worth losing this friend forever.