What does it mean when someone says “this is my very last straw”?

It is an expression that means something similar to 'you are on my last nerve' which means that you are driving me out of my mind

Explanation:

the last in a series of unpleasant events that finally makes you feel that you cannot continue to accept a bad situation: Losing my job was bad enough, but being evicted was the final straw. She's always been rude to me, but it was the last straw when she started insulting my mother.

Explanation:

the last in a series of bad things that happen to make someone very upset, angry, etc. It had been a difficult week, so when the car broke down, it was the last straw.

when in doubt choose c

it's what my teacher told my class when we were going into psats