drive (one) over the edge

1. To cause someone to commit to doing something they had been considering or close to doing for a while before. I tried to remain silent about my father's associations with the extremist group, but the events over the weekend have driven me over the edge. The constant train delays are what drove me over the edge, no pun intended, about buying a car. I suspect that Mrs. Patterson's generous offer to match donations is what drove people over the edge in the final days of the campaign.

2. To cause someone to suffer a mental breakdown. Following on the heels of her recent divorce, the death of her father drove Kate over the edge. I think all the pressures at work and at home finally drove John over the edge. The boss is gonna drive me over the edge if she keeps piling things on my to-do list like this. I'm already working 80 hours a week as it is!