In the first film, Kirby reluctantly joins the appliances on a mission to find Rob, who is referred to them as "the Master." While although seemingly cantankerous and bossy towards the others, he actually cares very much about them, and risks his life to save them more than once. Kirby cannot help but keep up the appearance that he is independent and being held back by the others.
Being grumpy and stubborn, Kirby doesn't hang around much with the other appliances until near the very end of the first movie. He utterly despises Blanky and his overly emotional personality. Kirby starts to soften up as the film progresses. In the movie's sequels, he is more laid-back and closer to his fellow appliances.
Kirby on cliff
Kirby in a bad mood
Kirby in the workshop
Kirby yelling at Lampy and Radio
Setting off out into the open world
Kirby pulling the others on the chair. Why he's pink isn't quite explained.