Just gonna establish the rules since this is a hot concept.>Eating bird person pizza causes girls to rapidly put on weight. This gets worse the more time passes and the more BP Pizza they eat.>The girls will quickly accept their size, loose their shame in their gluttony, view themselves as normal, and view themselves as attractive. This gets worse the more time passes and the more BP Pizza they eat.>These girls emit pheromones that will slowly inflict these changes on girls who haven't even ate the pizza. With just a few girls it's easily offset, but with enough converted girls and prolonged contact, the fatness takes in the air.>Boys are immune to the pizza itself, but those pheremones also turn them into chubby chasers gradually.
Let's say it starts with Morty taking a pizza from his world, asking Rick if it's poisonous or anything (Rick says no, Morty is a boy it'll just give him the shits. He only mentions the other part after Morty has left) and he gives it to Jessica in an attempt to win her favor.