Cowabunga

MAX: I’ve been in California.
LORELAI: Well, cowabunga dude.

Cowabunga, a phrase of unknown origin which was popularised (as Kowa-Bunga) on the children’s TV show Howdy Doody in the late 1940s and early 1950s, where it was used by a character named Chief Thunderthud as a fake Native American greeting [picture shows it as Cowabonga, just to confuse things]. It became associated with the surfing subculture, who spelt it cowabunga, and used it to express delight or satisfaction.

By the early 1980s it was used as a catchphrase by Cookie Monster on Sesame Street, and became more widely known in the late 1980s and early 1990s due to its use by the cartoon Teenage Mutant Ninja Turtles. Bart Simpson from animated series The Simpson gave it even broader recognition in the 1990s.

Lorelai presumably thinks of it as a particularly Californian phrase because of its use by surfers. It seems as if almost everyone who leaves Connecticut goes to California! Max is Lorelai’s second ex to move to San Francisco.