Montezuma's Revenge (var. Moctezuma's Revenge) refers to the conquering of the Aztecs by European invaders led by Hernán Cortés (1485-1547). Moctezuma II (1466-1520), the emperor of Aztecs at the time, was killed by his own people, in revolt against the Spanish invaders, so that anything bad that happens in Mexico to descendants from the invaders, or any non-Mexican, for that matter, could be interpreted as a posthumous "revenge" of the emperor against his enemies.

Originally, it is a colloquial American English name for traveler's diarrhea caused by a bacterium strain present in food and water, to which Mexicans are normally immune, but that causes disease in foreigners.

It is an expression with several meanings:

Montezuma's Revenge (medicine)
Montezuma's Revenge was a video game for console and microcomputer systems, published in mid-1980s.
Montezuma's Revenge mountain bike race in Colorado, USA.
Montezooma's Revenge is a roller coaster at Knott's Berry Farm.
The source of this article is Wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL
 

SOME GOOD ADVICE FOR TRAVELERS:
Don't drink tap water in any form (unless you know that it has been boiled sufficiently). Some beverages that are probably safe to drink include hot tea, coffee, and other hot drinks made with boiled water, as well as bottled or canned beer and wine. Note that condensation on canned or bottled beverages may be contaminated, so clean before drinking from them.
Omit ice cubes in drinks and foods. This means no ices and popsicles as well.
Pass up foods that were rinsed under tap water, such as raw fruits and veggies (i.e., salads). If you can peel the fruit yourself, it's probably safe to eat.
Avoid consuming meals that may not have been cooked or reheated enough to kill microorganisms, or are not served piping hot, such as lasagna, quiche, casseroles, and cold soups.
Don't eat any raw or inadequately cooked food, such as meat, seafood, and eggs. Note that some kinds of fish and shellfish still may not be safe to eat even when fully cooked because they can contain poisonous biotoxins.
Stay away from unpasteurized milk and other dairy products.
Steer clear of food and drinks from street food vendors.
Avoid brushing your teeth with tap water — use bottled or canned carbonated water instead.
Keep your mouth closed while showering, bathing, or swimming to prevent accidental ingestion of tap water.
Always wash your hands before meals, preferably using antiseptic or antibacterial gel or prepackaged wipes.

It's useful to talk with your health care provider about traveler's diarrhea and other travel health-related concerns, including required immunizations, well in advance of your trip. Make sure to discuss detailed information about the signs and symptoms of bacterial, viral, and parasitic traveler's diarrhea, prevention and preparation tips, and various treatments (antidiarrheal and antimicrobial drugs) to alleviate the symptoms and/or shorten the duration of the illness. For example, many travel medicine programs or clinics will give a prescription for antibiotics to take with you on your trip in case it needs to be taken at the onset of serious traveler's diarrhea. This has been shown to lessen the severity of diarrhea in 80 percent of people who get it. After meeting with your health care provider, you'll be informed and prepared in case it's not possible for you to see a provider or visit a health care facility, as the quality of medical care varies from country to country. Of course, if you're feeling extremely unwell, or if you do not feel better after several days, put your concerns aside and try to find the best hospital possible in your destination for medical attention as soon as possible.

Dehydration is the main concern when traveler's diarrhea climbs on board, but it can be prevented. If you happen to get traveler's diarrhea, drink plenty of fluids, even if you're not thirsty, to avoid the dehydrating effects of diarrhea. Bottled or canned carbonated water or other soft drinks that do not contain caffeine (as it can exacerbate diarrhea) are usually safe to drink. Avoid any alcoholic beverages. If you have no appetite, don't eat; if you're hungry, first try non-greasy, low fiber foods that are not too sweet. As you get better, switch to some soft, bland foods, such as bananas, (plain) rice, applesauce, and toast (a.k.a., the BRAT diet). Boiled potatoes, salted soda crackers, cooked carrots, and skinless and de-fatted baked chicken are other good possible options.

If you do become dehydrated, you may need to drink a special oral rehydration solution (ORS) beverage to restore your water and electrolyte (salts, such as sodium and potassium) balance. You may want to bring along some pre-prepared packages of ORS powder with you on your trip; they are available at some drug stores. For more specific information about ORS, talk with your health care provider.