Hardware makers: What's your worst "I can't believe I missed that" PCB moment?

Building hardware is brutal. One tiny mistake and you've got an expensive paperweight.

I once ordered 50 boards with a wrong footprint. $600 gone. Three weeks wasted. That sick feeling when you power it up and nothing happens.

Would love to hear from other hardware folks here:

What's your worst PCB disaster story? Wrong footprint? Missed connection? Magic smoke?

(Working on something to help with this—launching today actually—but genuinely curious about your experiences!)