Another fun thing is that calling someone you don't know "thou" used to be an intentional insult ("you're not worthy of being called 'you'"), something that might be missed by a modern reader of Shakespeare or other EME texts.
It's interesting that in Viennese German (my German is terrible but I do at least try) it seems like the informal form is the default, in a shop I get asked "Braucht du hilfe?" rather than the formal "Kann ich Ihnen helfen?".
Maybe this is what they mean when they say people in Vienna are rude, but coming from Scotland using informal language even in fairly serious settings just seems comfortable and normal.