#very sad...

I think you know how the etiquette works when you talk to someone standing in front of you. Use “Sie” whenever you want to address someone formally and/or a stranger. May it be an older person/the parents of a friend/your manager/the cashier in the supermarket/etc. Continue using “Sie” until someone gives you permission to say “Du” and use their last name until they again give you permission to call them by their first name. If you came that far you made an acquaintance. Nothing more, you aren’t friends with them or anything, don’t mistake that. Most of the time they just feel old.

It’s actually not the same in the internet. If you, for example, visit a forum and talk to somebody there you’d never say Sie. Except if that person is someone YOU consider “above you”. That can be for example someone who knows A LOT more about the stuff you are researching or a mod or anyone. In that case you’d address them formally, though most of the time they will say “du” to you. After they address you informally you might as well. But always do what you feel is right. Nobody will be angered by it, even though if you do it for a whole conversation they will think that you must be raised very, VERY strict.So no, you use Sie for people YOU think are higher in the hierarchy and Du for everyone.

There is still some more, but you asked, lol. This one applies for both - Internet and Real life interactions. Should you get in an argument and the other person uses “Sie” you can decide if you want to be one of that awful youngsters who are to cool for etiquette or you use it too, like you should. That person is either trying to 1.) Calm the situation (It’s like a dog showing it’s belly; they put themselves beneath you by addressing you more formally) or 2.) Stands above it (He doesn’t really want to discuss it, bc he’s way to stubborn and will stand up for his point of view). Most of the time it’s the first reason, tho. In that case do not, I repeat, do not use “Du”. That would be so disrespectful and provoking for the other person.

If you are writing an e-mail or letter and it’s not to a friend or mutual, always “Sie, Ihnen, Ihr, Ihrer, etc” - and most important: Capitalized. That doesn’t apply if you address yourself or somebody else. You only capitalize when you address the person you are writing to, which you don’t know.

In any case: If that person doesn’t want you to address them informally, they will tell you. It will be REALLY awkward for you and even though you can always tell anyone you want to, to not address you informal, it can happen that if you clearly are under 18 people will not say “Sie” to you since you are not an adult. Just keep on insisting that you don’t want to be degraded, they will eventually give in. If you accidentally say “Du” to someone you shouldn’t just quickly apologize and correct yourself, so they don’t even have to tell you to address them formally.