When you awake to a fellow bending over you in the "toilet position" with his balls in your mouth and a fart escaping out his arse on to your eyes. Popular on stag do's. This was named due to the similarity to the warm Mexican air and salty taste in your mouth.
When there aren't any whole tortilla chips left and just a bit of salsa left in the bowl, one dumps the remaining chip fragments into the salsa bowl, stirs it up and eats the rest with a spoon.
Pass me the chips..." "There aren't many left. It looks like Mexican breakfast cereal time.