Whilst at a previous employer, (a West Yorkshire based manufacturer of consumer electronics products of a tele-visual nature), the management decided that because targets had been met, it would give the workforce a company sweatshirt each.
The following morning, our PCB functional test failure rate shot through the roof. Most of the products were VLSI based and quite static sensitive. We were well aware of this, and regular anti-static control audits were normal, making sure that everyone was wearing a wristband and heel grounders when on the factory floor.
It turns out our loyal production line staff had decided to wear aforementioned sweatshirts en masse. No one had even considered whether the material was suitable for a mass production environment involving delicate microelectronics. Turns out they weren't.
Urgent request to remove sweatshirts issued - defect rate returns to normal.
Anonymous - because some of those products are still out there, but could be "walking wounded" - a CE industry term for static damaged silicon which operates normally for a while.