Perhaps we may (regrettably) go down that road someday and perhaps there are instances of police overstepping their bounds to regulate "proper" speech, but I'd be willing to bet* my next pay check that being arrested for calling somebody a goat fucker would not hold up in court.
* - OK, not my whole check but like $5
If you called a judge a "goat fucker" in their court room, I suspect you would be in some hot water.
One could argue there's not a huge leap between rules/laws requiring respectful behavior towards judges in a court room and a law requiring respectful behavior towards world leaders...
Edit: Not sure why I'm being downvoted -- I'm not defending the German law, just pointing out that it's not that different from contempt-of-court punishments in the US.
Now, in an unfortunate turn of events should Cruz become POTUS I don't know if such a statement would be seen differently because I'd believe that he does do that.
Here's a girl in the United States who had a judge raise her bail just because she said "adios" instead of "bye", and then put her in jail for a month for saying "fuck you": https://www.youtube.com/watch?v=0rrRGhvpEjo