(The) Straw That Broke the Camel’s Back

What does the idiom “(The) Straw That Broke the Camel’s Back” mean?

Definition:

A final difficulty that exhausts someone’s patience or causes the collapse of something

For example:

“When Carlene asked for a vacation after doing no work for three weeks, that was the straw that broke the camel’s back. I fired her.”

Notes:

You can also say “the last straw.”