spit (out) the dummy

To have a childish overreaction or angry outburst to a negative situation or outcome; to act in a bad-tempered manner, likened to a temper tantrum of a child. "Dummy" here refers to a plastic teat used to soothe teething infants (also called a "pacifier" in the U.S. or a "soother" elsewhere), which they may spit when in the middle of a tantrum. Primarily heard in Australia. John spat the dummy when I told him I'd sold his old comic book collection. Don't go spitting out the dummy just because Cheryl got the promotion instead of you.

If you accuse someone of spitting the dummy or spitting out the dummy, you are accusing them of behaving in a bad-tempered and childish way. He spat the dummy when his wife decided to go back to work. They are taking the money but not talking to us. If they want to spit out the dummy, that's their affair. Note: The image here is of a bad-tempered baby spitting out its dummy.