MEME REFERENCE

Worst mistake of my life

Use immediately after a bad choice backfires, especially when the regret is obvious and the consequences are already chasing you.

What it expresses: A voluntary decision is followed by instant recognition that it was disastrously wrong.
Example: Seconds after volunteering to coordinate the reunion, fifty relatives begin sending conflicting requests, and you post this.
When not to use it: An unavoidable accident happens despite a careful decision; calling it your mistake would assign responsibility inaccurately.