Working on a breadboard, not using ICSP, so pulling the chip every time you program, it's easy to plug it in backwards, which reverses VDD and VSS... Once I couldnt figure out why my circuit wasn't working, I was probing around with a multimeter and everything. Then I looked up at the power supply and it had the overcurrent light on... with the current pegged at 2.5 amps! The PIC was connected that way for a total of about one minute, and it got hot enough to burn my finger when I touched it. And yet, when I flipped it back around, it worked fine. The only time I've ever succeeded in killing a PIC was powering it off 12v accidentally...