It was the last straw that broke the camel's back.
There is a limit to everything and people can only take so much before they snap. We can load a camel’s back with lots of straw, but finally the amount will be too much and the camel's back will break. And all it takes is a single straw that breaks its back - the last straw. This proverb can be applied to many things in life. People often exclaim "That's the last straw!" when they will not or cannot accept any more of something.