I don’t speak German but from the examples you’ve given I would say that the German and the English usages are similar, but not identical. In English, it’s almost always a rebuke, rarely a warning. It refers to forgetting about social rules, and your place within them. Should our expression be strong or calm depending on our tone, speaker, context, and the tone of voice, music, and expression?

In your examples

John, we’re going out to dinner tonight, john, john, us going out to dinner tonight. What would you do if you forget your self?

Is it fair to call this rebuke? I have behaved badly with John at school and the speaker was gently requesting that he control himself tonight. What would you do if someone felt superior to John or it was a desperate plea from someone who feels slightly inferior to John, she should be sent into the care of the Lord.

How to forget yourself?

A big rebuke from a social equal or superior. What do we do when we’re surrounded by angry people?

I miss myself. In moments too. I haven’t offered you a drink yet, and my friends refuse me and I am not talking after all the conversations about getting a drink!

Does the speaker ever admit his own mistake and have another speech for it? Is this a self-rebuke, although tone of voice and context will show how embarrassed the speaker feels over the faux pas.

What is context? Why is the expression almost never used in isolation? The third one is probably the most common, though.

Are they meaning threat or warning in German? How, if not, for it?

What is the best way to watch a person die and die, but that is too late for all kinds of people. In English, such a threat would usually wrap up in a few words. I’m a gentleman and I don’t stop, I probably’ll forget that, but I’m just a person. Similarly to the second example above, the person is trying to stay within the rules, while making it clear that he finds the other person’s behaviour unacceptable. ” As social rules erode, this usage becomes increasingly old fashioned.