I learned this one growing up in Texas and, subsequently, living in Los Angeles: always use the 'usted' form when speaking to a Spanish official. Mexican border patrol cops don't like it when you call them 'amigo,' give them a hardy pat on the back, slip a $20 in their pocket. No bueno, it doesn't fly. By the way, those of you not laughing at that obviously took French in high school, and that was a gay choice.