As the saying goes, "a little knowledge is a deadly weapon ." When I went to study in Spain, many years ago, I couldn't speak that well, but I knew the basic rules of grammar. One is that 'generally' nouns that are feminine end in the letter 'a'. Well, I wanted a chicken sandwich and since we generally eat hen, I applied that rule when I ask the deli worker "Quiero un bocadillo de polla." After a minute or two of his staring at me, my memory flashed back to what my more experienced roommate had taught me. pollO is chicken BUT pollA is a very vulgar way to say penis. Needless to say, I clucked like a chicken to clarify the situation.
Not quite so embarrassing but annoying was when I was in Israel. I was constantly turning to see who was calling me since the short form of my name Kendrick is Ken - Hebrew for yes.
