Answer: Paulette
Having been treated badly by Johnny throughout nearly the entire film, Paulette finally turned on him during the talent show, when he forbade her to go out on stage in her skimpy summer outfit. This was the final straw, and Paulette really let Johnny have a piece of her mind when she declared angrily that she was the best he was ever "gonna get, so" he had just better "take it or leave it". A stunned Johnny was considerably chastened by this outburst, so much so that at the end of the film he sang to her, "I like what you got, I guess it's okay if you want to show it".