Finest Hour
Period in a persons life where he/she does his/her noblest deeds in life. Used especially in World War I and II, where thousands of soldiers answered their call of duty to their country. Is not used when acts are not "noble" or are inherently evil.
Thousands of Allied soldiers answered their country's call. In battle, it was their finest hour.
My Finest Hour
When I lose everything.
It will be my finest hour.
not my finest hour
to acknowledge a blunder, mistake or bad decision.
Someone: You were fired last year for telling your boss to go fuck himself?
You: Yes. It was not my finest hour.
You: Yes. It was not my finest hour.