There are two different words in the German language that translate into the word "you" in English. One of them is a formal word, that is being used when you refer/talk to someone you don't know that well or as a form of respect. The other is being used by friends. The former mostly is connected to you referring to the other person as Mister (Lehmann). And this is where one of the jokes of the movie lies. The use of that word and something might be impossible to translate (I have no idea how one would try to).

That might have been a lengthy explanation to a simple joke, but hopefully it also made clear, how the humor of the movie works. And a former VJ (MTV) is in the center of it all. Watching him take his first steps into "major" acting and succeeding is more than satisfying.