No specific mishaps that I can think of as a result, but I was never able to pronounce the German word for “night” (I always say “naked”), or the Italian word for “pen” (I always say “penis”). People got used to me saying things like “It is a very clear naked” or “May I borrow your penis” after awhile, though.
I was with an American and French Canadian friend in Italy (the French Canadian spoke excellent english), and we were talking with some German girls (who also spoke very good english) at a bar. My American and French Canadian friends had gotten drunk on a tour boat the night before, and were discussing their antics, when one of the German girls (confused at the conversation, which was laden with inside-jokes) asked something along the lines of “Is boat drunkenness some kind of cultural joke between Americans and French Canadians?” My American friend immediately replied, “Oh sure, there are lots of inside cultural jokes between Americans and French Canadians. Like, ‘hamburger.’” Taking my cue, I immediately burst out in uncontrollable laughter, tears streaming down my face, screaming “Hamburger! Hamburger! Oh, that one gets me every time!” The German girls looked quite perplexed, which caused the French Canadian friend (who quickly realized what we Americans were up to) to also burst out laughing, which only added to the Germans’ confusion. I don’t know if this would be better classified as a foreign-language mistake on the part of the Germans, or a cruel joke on the part of the Americans/French Canadian.