Google has the answer

It turns out, there’s a name for that phenomenon: the online disinhibition effect, or “the abandonment of social restrictions and inhibitions found in normal face to face communication when on social media. In other words, it’s the tendency for otherwise decent humans to engage in aggressive or obscene online behavior.
Phew!
Now I know the real reason why I had to block five users and delete eight mail on only my first day here.