= the last bad thing (even a small, minor bad thing) in a series of bad things that finally makes someone very angry and/or take action
*the literal idea being a camel carrying a large amount of hay and by adding one more small straw of hay it finally broke the camel’s back
Ex: I’ve had a bad week, but the bird pooping on my head was “the straw that broke the camel’s back.”
Ex: After making many obscene phone calls, he later threatened her son. For her, that was “the straw that broke the camel’s back,” and she called the police.