Fill in the blank with suitable words.
That’s the ____ straw. I won’t be able to tolerate this anymore.

‘That’s the last straw’ is an idiom.
Meaning: a further difficulty or annoyance, typically minor in itself but coming on top of a series of difficulties, that makes a situation unbearable. 
Ex: His affair was the last straw
Therefore, option 3 is the correct answer.