One norm I think should be part of the norms in this digital world is respectful disagreement. I don't think everyone should have to agree, but I don't think being disrespectful or immediately dismissing someone because you disagree with them. There should be conversation. That is how everyone learns and advances.
I also think knowing when to be professional and when being casual is acceptable. I find students often struggle between friends and school expectations, especially when communicating online.