Have kittens
Definition 1 of 1
Pro Tip 1/3Strong Emotion
Expresses a strong, often exaggerated feeling of unhappiness or worry. 
She's going to have kittens when she sees the chaos in the kitchen.
Pro Tip 2/3Informal Setting
Used in casual conversations, not in formal writing or speech. 
If I lose his book, he'll have kittens!
Pro Tip 3/3Hyperbole
Often an exaggeration, not meant to be taken literally. 
You're going to have kittens over such a small dent in the car?