The cop should have done his job: Written the ticket and otherwise shut up. The police exists to enforce the law, not parent. Although the fact that he's dealing with a foreigner makes me wonder if the cop knows a ticket won't work. It could be that the ticket wouldn't be valid in Germany, so the cop is resorting to intimidation. I know that European countries have to engage in some diplomatic traffic legislative co-op yadda-yadda before tickets from one country are valid in another.