At first, Rex lived on the safe side by pointing out everything that was wrong or unsafe about a situation. When Rex popped that huge bubble and said that it would make the floor all wet, his friends started calling him Party Pooper Rex. He did not like the nickname what so ever.
Later in the video, Rex is in the bathtub with all the other bathtub toys and all they want to do is party, but when the drain gets rid of all the water, the toys are unable to move around and party. They needed someone with arms to turn the water back on and Rex was the only one who had arms so he did what they asked. Once the water was on, the party started becoming out of control and Rex was the life of the party. In the end, the tub overflowed and ruined the bathroom, but all the bathtub toys fell in love with him and he was know as Partysaurus Rex, not Party Pooper Rex.
Rex showed leadership by jumping out of his comfort zone. He has always been the safe-side toy and when he finally let go and decided to have fun, he developed a reputation amongst other toys (people) in his community. In order to be a good leader, you must not be afraid to try new things and put yourself in uncomfortable situations. By trying new things and jumping out of your comfort zone, you begin to grow as a person and a leader. Leaders shouldn’t be afraid and even if they are, they shouldn’t show it to the people they are leading. When you are in an uncomfortable situation or dealing with something that you have never dealt with before, that is where true leaders shine. They adapt and prevail. That is what Rex did and that is what he is known for now.