Insulting people is a crime in Germany. If you said "Hitler was a poopy head" that'd be illegal. But they wouldn't bother to enforce that. If you say it about a real person, they can press charges.
fyi: insult is a so called "Antragsdelikt". That means authorities can only press charges when the victim files an official complaint. Otherwise they can't do anything.
Which also means they wouldn't be able to do anything about you saying "Hitler was a poopy head".
Which also means they wouldn't be able to do anything about you saying "Hitler was a poopy head".