cow

have a cow become angry, excited, or agitated. North American informal

☞ The reference is probably to the eye-watering pain that would be caused by giving birth to a cow.

1990Susin NielsenWheels 'Don't have a cow,' she said huffily. 'It's no big deal.'

a sacred cow an idea, custom, or institution held, especially unreasonably, to be above questioning or criticism.

☞ Sacred cow originally referred to the veneration of the cow as a sacred animal in the Hindu religion.

2013New Zealand Herald Everyone knows it's time New Zealand started thinking smarter. That extends especially to the sacred cows like our targeted benefits system.

until the cows come home for an indefinitely long time. informal