firstlast is right. Most funny word is "Handy" totally english word used as a noun for mobile phones in Germany. Nobody really knows how that happened - apart from them obviously being handy. But the best part is, that english native speakers are starting to call a mobile phone a handy too. :D
This is a good discussion. Some words fall into the category of "borrowed words", meaning that they have been adopted into our language from another language without undergoing any kind modification (Doppelganger is another example, also from German). We could go even more in depth here and discuss what actually constitutes a "borrowed word", since some words that are accepted as English words are very close, if not identical to the words they came from in another language, but this probably isn't the right place to do that.
I'm with Ventifact on this. Would you call bungalow a Hindi word? It is a loan word from Hindi. What about disco? It is borrowed from French, but shortened from its original form discotheque. Actually what is an English word, as many or most common words are derived from Latin or Norman French, and some from the Celtic languages? Kindergarten, schadenfreude, sauerkraut and angst are English words with German roots.
(Five years and he doesn't learn to not leave the soda in the fridge?)