Legend has it that the name came from the rowdy surfer and skater kids who would hang out at the original In-N-Out location in Baldwin Park, California in the 1960s. The employees referred to them as animals because of their raucous behavior (In-N-Out employees are notoriously clean-cut), and after they started ordering mustard grilled burgers with grilled onion, spread, and pickles, that sandwich took on their name: the animal style burger.