I was in town last week, wandering down the main shopping street, when I caught notice of a conversation going on next to me in English. I slowed down long enough to notice that the speaker was non-native, most likely German, probably not older than 18. She was talking to a girlfriend of about the same age, most likely a non-German. I caught references to a "he" in the conversation and gathered that she was complaining about "him". Then, the German girl said to her friend, "you shouldn't always have to stick it up his ass". At that point, I was past the girls, so they could not see my smile as I tried to suppress laughing out loud. I knew right away what the poor girl was trying to say, but oh did she fail! I wonder what her non-German friend thought of her. Today, I told my son about what I had heard, and he burst out laughing. So, here is the explanation for those of you not fluent in German.
In the context in which it was used, the girl was trying to say that you shouldn't have to spoil someone or spoonfeed something to them. The German expression, granted vulgar, but frequently heard even among educated people is "jemandem etwas in den Arsch schieben", literally translated as above by the clumsy German girl. Most native English speakers might have thought the German girl was trying to say something like "shove it". But no. There are variations such as "stuffing sugar/powdered sugar up someone's ass [jemandem Zucker/Puderzucker in den Arsch schieben] that give a better hint at what is intended. In any event, I've made my point. Now that you've got the idea, don't think that if someone tells you, in German, to "lick them in the ass", that they are offering to share their powdered sugar with you. "Leck mich am Arsch" has about the same meaning as you would expect it to in English: "Kiss my ass."
Sorry for this vulgar post, but better a vulgar one than no post at all -- that's my reasoning.