Not me, but a friend. In high school the best computer in the school was a 386SX. They decided to upgrade it to a DX by adding a maths co-processor to the main board. So the ordered one, and when it arrived, they gave it to my friend to install for some reason. Now, the chip had one corner cut, which you are supposed to line up with the cut corner on the socket, so you know it's seated the right way. Of course, my friend put it in completely backwards (because it fit an any direction.) So he tries to boot up the computer and nothing happens. So he looks at it again, and realizes the chip is in backwards. So he turns the box off, pulls out the co-processor, rotates it 180 degrees and puts it back in the socket. Unfortunately, misfiring it in the wrong direction had toasted the chip completely, and when he put it into the socket in the correct orientation, the socket locked itself shut, as it's supposed to do. But, since the chip was fried, this effectively locked the motherboard in an unbootable configuration with a dead shop.
Sigh.
