Once too often
Definition 1 of 1
Pro Tip 1/3Risk and Consequence
Use when describing a behavior that's risky, which eventually leads to a negative outcome. 
She skipped class once too often and failed the course.
Pro Tip 2/3Ending Tolerance
Indicates the last instance of behavior that destroys remaining patience or acceptance. 
He arrived late once too often and was fired.
Pro Tip 3/3Behavior Threshold
Suitable for when someone exceeds the acceptable limit of an action or behavior. 
You've ignored my advice once too often; I won't help anymore.