Why did Ron want to be a Cheerleader? Why did Ron want to be a Ballerina for Halloween? Why did Ron like wearing a skirt when he was in Kim's Body?
Well, the answer is simple yet complex: Ron...wants to be a girl.
It started out at a young age, when Kim and Ron spent their first Halloween together. They decided on a Ballerina and a cowboy costume, but to Kim's surprise, Ron wanted to be the Ballerina. This was looked at as nothing, just a boy who was confused.
Ron always seemed to be more in touch with his feminin side, he would play with Kim Possible more than with the other boys at school.
Reaching his Teens, he was drawn to feminine things more and more, he would sometimes try on Kim's makeup, or let Kim apply it. It was during high school that Ron began dressing like a girl. Many things happened to him and Kim during their teens, mostly Kim's hobby of saving the world from different bad guys. When their brains switched, Ron finally experienced life as the fairer sex, but when they switched back, Ron felt devestated on the inside.
When Ron had to pick an extra curricular activity, Kim gave him the idea of Joining the cheer squad. Here's where fate spilts, while the Ron Stoppable you know changed his mind and opted to be the school mascot, the meddling of one Bonnie Rockwaller put Ron on a new path
Planning to humiliate the boy, Bonnie, with the other girls, force Ron into a girl's cheer uniform, with wig and makeup. However, instead of Ron being embaressed and shocked, he was excited.