the last (or final) straw a further difficulty or annoyance, typically minor in itself but coming on top of a whole series of difficulties, that makes a situation unbearable.

☞ The full version of this is the proverb the last straw breaks the camel's back. The modern form is traceable to Charles Dickens in Dombey and Son (1848), but earlier versions are recorded, including a mid-17th-century reference to the last feather breaking a horse's back.