When Rex accidentally breaks up a party in Bonnie's room due to his clumsiness, Mr Potato Head jeeringly refers to him as "Party-Pooper Rex."Shortly afterwards, Bonnie chooses to bring Rex along for a bathtime adventure. After the bath, the other toys in the bath lament how it feels like the party ends when bathtime is over.Wanting to redo his image, Rex declares himself to be "Partysaurus Rex," and starts to fill up the tub with water. The other bath toys eagerly cheer on his efforts, but their enthusiasm soon cause a huge bubble bath/rave to take place.Realizing he may have gone too far, Rex attempts to turn off the water, but the faucet tap comes undone. His attempts to unplug the drain fail as well. In a last ditch effort, he pulls the lever on the faucet...only for the water to stop there, and the shower to come on!The others cheer on his efforts, as the party is washed over the side of the tub, and floods out into the house!In the aftermath, Rex revels in his new persona. Though Potato Head laughs it off, the outdoor toys call on Partysaurus Rex's services, and Rex happily complies, giving his friends a hearty, "Duty calls!"