1. become enraged or very angry, or be ecstatic or very excited
he'll flip out when he hears the news
To flip out is a colloquial American phrase which can mean either to lose one's temper or lose control over your emotions (in a positive way). This is a very informal phrase you are more likely to use with friends or family. Similar expressions are ‘to lose the rag’, ‘to lose it’, and ‘lose your temper’.