-noun
The unfortunate occurrence of a bowel movement that crests the rear band of an infant or toddler's diaper, resulting in yellow, curdy staining of the child's back and clothing (and often furniture, parents, and household pets).
Etymology: from the practice of running from Europe and crossing the Atlantic Ocean to The Americas
Date: 2009
usually offensive : a European who enters Anahuac
Similar to "Fives" or calling "shotgun", "Quack Quack Seatback" is a common way to lay short-term claim to a seat you're about to vacate when with a larger group. Sometimes shortened to "Quacks."
Person A: "Hey, you stole my seat."
Person B: "It's my seat now."
Person C: "No, he called Quack Quack Seatback. Move it."