I hereby announce a new acronym
INEB (i'm no expert but..)
INEB
I think that when the Spaniards went over 'visiting' South America, and Mexico in particular,they happened across the Aztec civilisation and it's King Montezuma. The outcome of these 'visits' was basically the end of the Aztecs! Now when a foreigner (particularly a Spaniard) eats abroad, and contracts diaorreah (is that spelled correctly?) it's colloquially seen as divine retribution for the obliteration of the Aztecs - hence Montezuma has his revenge