Flipping one's lid is a commonly used phrase to express the sudden outburst of emotions. If you are looking for some alternative phrases that convey the same idea, there are several synonyms that you can use. You can say that someone has lost their temper, blown a fuse, hit the roof, gone bonkers, lost it, become unglued, or gone ballistic. These expressions are more polite and appropriate in formal settings than the original phrase, which might be considered crude or offensive. So, whether you are dealing with a difficult situation or trying to express your own emotions more appropriately, these synonyms will come in handy.