last straw, the

The final annoyance or setback, which even though minor makes one lose patience. For example, I could put up with his delays and missed deadlines, but when he claimed the work was unimportant--that was the last straw! This term is a shortening of the straw that broke the camel's back, which conveys a vivid image of an overloaded animal being given one slight additional weight. The expression dates from the mid-1800s, and replaced the earlier the last feather that breaks the horse's back.