1. Taurus 94 .22lr Revolver - cylinder would bind up, effectively jamming it.
2. Olympic Arms K9GL Carbine - every type of malfunction in the book despite 4 trips to the gunsmith and 1 back to Olympic Arms. A client was shooting it and it almost blew up on him. I sold it to a gunstore who said they would fix it and resell it. It sold and then was back on their shelves 2weeks later.
3. Mossberg 500 Home Security .410 Shotgun - would not work with .410 handgun rounds(although it should have) and then would not work with regular .410 shotgun loads(pump action would seize up).
Browning Hi Power, the Ultimate 9mm