usually at a high school football game or other public event evolving teen aged girls and fall weather. Involves a large group of the teen aged female population wearing skinny jeans, leggings, yoga pants, or other types of very tight pants that show a defined booty. Usually they are also wearing hooded sweatshirts.
there is also a 2% margin for error in this, the girls wearing sweatpants.
guy 1: hey dude were you at the football game last night?
guy 2: yeah dude there was such a bootypocalypse, i almost overdosed on booty
guy 1: dude i know, did you see girl 1
guy 2: Yeah man those leggings gripped her booty deliciously.