That's the last straw!
I'm never going to see him again!
Straw is dried grass in strips. The full idiom is the last straw that broke the camel's back. Rather a cruel idea but the concept is that the weight builds up until one small piece does the damage - the last straw!
So when you've been tolerating something for a while but you reach the point where you can't any longer, that's the last straw.
I googled camels and came up with this. Camel is also a famous brand of cigarette, you know, the brand smoked by doctors?