What are some of the rules about the Internet that were taught to you but are now completely ignored?
For me, it was that the Internet never forgets and that you should never enter your real name. In my opinion, both of these rules are now completely ignored.
Sticking around and "lurking" for a bit before you try to engage with a new community, to learn the local etiquette before you make an ass of yourself. Or at least reading the rules as a bare minimum.