It's easier than you might think to try to deliver a compliment about a person's looks in German, but end up asking them to undress and, despite the lack of fuss Germans may generally make about taking off their clothes, this might not go down so well in a bar.
Cafés can also be surprisingly dangerous places for ladies with an eye for a handsome barista. A Freudian slip can turn a request for a latté into asking for a Latte, which can only end badly in a public space.
The German language, while beautifully precise in many ways, fails to draw the crucial distinction between male friend and boyfriend, and female friend and girlfriend.
And don't ever remark on feeling the temperature when on a date until you're totally certain you've got the reflexive completely straight in your head - otherwise feeling a little warm translates to being horny, while a bit of a chill turns to frigidity.