1. Colt Mk IV Series 70, also known as the "Jammamatic." This pistol made me vow NEVER to buy another Colt . . . not because it malfunctioned, but because the <expletive deleteds> in Colt's factory NON-service would NOT fix it. Oh, they claimed - repeatedly - that it had been fixed, but rarely would it fire a full magazine without jamming. Typically, it would jam at least 3 or 4 times. Blah!
2. Kahr P9 . . . make that a POS9. What were the problems . . . premature slide lock, failure to go into battery, failure to engage the striker when the trigger was pulled, trigger pin walking out . . . Kahr eventually replaced it, putting them head & shoulders above Colt's when it came to honoring their warranty, but I immediately traded the replacement - unfired - for a Glock 26.