Rule #2: Chile goes on everything. Add to the above list: mangoes, ice cream, popcorn...
Rule #3: Your quesadilla may or may not have cheese in it, and same goes for your taco. I have yet to find a distinguishable difference between these two menu items, but your beer will come in two distinct varieties: clara (light) and oscura (dark).
Rule #4: You will get sick. But that's probably just because the street tacos are so damn good.
Rule #5: Ordering anything "a la mexicana" not only means that it will be in the national style but that it will literally be painted in green, white and red sauces. Alternately, inviting someone to eat "a la americana" means that you will each pay for your own meal.
Rule #6: Eating Mexican food will not make you fat. Eating Mexican food made with over-processed American ingredients will.
Rule #7: Lunch is the biggest meal of the day. Failing to eat soup, rice, beans, quesadillas, a main course and dessert all in one sitting means you don't like the food.
Rule #8: Corn is still very much a dietary staple. Beans, however, were just taken out of the basic basket of consumer goods and are now considered a luxury item.
Rule #9: At Sanborn's, an Appleby's-type chain restaurant, you can not only order food but buy electronics, stuffed animals, porn and airline tickets in the accompanying store.
Rule #10: When ordering sopa (soup) it may or may not have liquid. A sopa of arroz con pollo is just a regular chicken dish.