Alle wissen, wer sich unmöglich verhalten hat.
can anyone help to find out what is "sich unmöglich verhalten"?
"Sich unmöglich verhalten" means "to behave in an unacceptable manner".
For example, someone went to a wedding party, got drunk, and yelled at people and told dirty jokes all the time. Then his wife might say on the following day:
Du hast dich gestern wieder unmöglich verhalten!
Everybody knows who behaved impossibly.
sich verhalten - to behave (your)self
someone please correct me if I'm wrong
Its somehow correct. But I'd rather translate it as "who behaved terribly" or "who behaved unbelievably".