I've faced one article devoted to online transgressions. Let me tell you briefly about them.
1. You forget to answer an e-mail
You have forgotten to answer your friend. it's ok as… if something serious happend she would give you a call. Right?
2. You fail to accept someone's friendship/follow them back
Sometimes it happens.
3. You call someone back without listening to his or her voice message first
Hey, at least you didn't respond to the voice message with a text message.
4. You don't respond to a text message in which there's no question
Totally OK, unless that statement is akin to „I need a kidney NOW!“
5. You quietly unfriend someone you don't really talk to anyway
If they get angry and contact you, you can always whip out that „you don't really talk to me, anyway“ thing.
6. You miss a friend's event because he invited you on Facebook
What about phones?
7. You „unsubscribe“ from a listserv
Sometimes, friends and exes add us to their mailing lists against our will. And often, we are annoyed by that influx of e-mails — especially if we're estranged from said friends/exes. Feel completely free to hit „unsubscribe“ in those cases. Your in-box, yourself.