RORY: Where does Dad have a misspelled tattoo?
LORELAI: Ah, ah, another story for another time, possibly before your first trip to Mazatlán.
Mazatlán is a city in Mexico, located across from the tip of the Baja California peninsula. It is a popular tourist destination, famous for its beach resorts. It’s a popular destination for American students to go on spring break (less so now than formerly). Lorelai is saying that once Rory is a young adult and preparing to make her own drunken mistakes, she will be ready to hear about her father’s tattoo.