Miss Piggy has a temper tantrum and is in a bad mood. She complains and yells at various people for little things.
Later on, she's stuck in the elevator along with.........Lips. She and Lips talk and Piggy opens up to him. He discovers everyone has forgotten her birthday because they've been too busy with the show. Lips and Piggy form a stronger bond, and Lips tells Piggy to apologize for her behavior and explain to everyone why she's been in a bad mood for the day.
The reason why I suggested Lips is to get the character more exposure.