The last straw.
The straw that broke the camel's back.
The last of a series of annoyances or disappointments that leads one to a final loss of patience, temper, trust, or hope.
Also, a barbarian of the Hyborean Age possessing a penchant for punching ill-tempered camels in the head and rendering them unconscious.
"Alright, that's the camel breaker. You've had this beating coming for a long time, and here it is!"
"My jerkface boss took credit for the project I'd been spearheading for the last four months while he played golf, and that was the camel breaker, so I told him where he could shove my job and then told his boss who REALLY completed the project."
"Quickly, quickly! The Camel Breaker is coming! Get your camels in off the road before one of them spits at him and ends up with a broken head!"