A saying in an up and coming popular internet dance song of the same name. It means when tourists and travelers visit Mexico for any type of festive, partying situation. It could be Spring Break, New Year's, Mexican Independence Day, 4th of July, Halloween, Cinco de Mayo, St. Patrick's Day, St. Valentine's Day, pretty much any reason to drink copious amounts of alcohol and dance.
Mark: Dude, Spring Break was totally rad!
Veronica: For shore, we totally gotta Sexico Mexico again next year!