breaking point
1. Literally, the point at which an object or machine ceases to function or falls apart. Don't put anything else on that chair—it's wobbling and looks to be close to the breaking point. Based on that terrible noise, it sounds like your car is at the breaking point.
2. By extension, the point at which an overworked or overburdened person, system, organization, etc., fails, give ups, or collapses. I was already fed up with my husband's lazy, selfish ways, but his refusal to come with me to my mother's funeral was the breaking point. With governmental resources already strained to the breaking point, any sort of environmental disaster would likely be catastrophic.