Jennings 380. I was young, dumb and didnt know better. I ended up trading the gun for a pizza from Union Jacks, needless to say, I got the better end of that trade.
HAD a Taurus pt-22 once. Not sure why I bought it at the time? I had not shot it all that much and the action was getting pretty sloppy so was one of the few guns I ever got rid of and did not feel bad about afterwards.
Interarms PPK .380..... put about 100 failed rounds through it, jams all the time... it now serves its purpose as a paper weight on my money in my safe...
My worst purchase was a pair of brand-new Taurus Airweight .22 revolvers. They would lock up when trying to fire them. I sent them back to Taurus FIVE times each before Taurus finally replaced them. I sold the new guns as soon as they came in and went back to S&Ws. I thought these might make some nice inexpensive training guns but I was sadly mistaken.
Jennings 22 cal, POS. Squires Bingham M16/22 cal, POS. Intra Tech 38 spec Derringer w/grip safety, POS. All cycled one round, jam, cleaned, jam, jam, jam. Adios POS.
Intra Tech shot okay till I was cleaning and a piece of metal fell out of it and I couldn't figure out where it went. Feared taking apart the grips that it would fall apart. Funny, traded the Intra Tech for a Davis 32cal derringer which is pretty cool gun. Haven't shot the Davis more than a dozen times, but it is holding up ok for a safe queen that is nickle plated w/ wooden grips. It serves as a BBQ gun.
A 1988 Helwan 9mm - licensed Egyptian knock-off of the Beretta Brigadier. I accepted it as credit against some money that a guy owed me, and I really should have held out for cash. Wouldn't feed, wouldn't eject, you had to remove the mags by force and it was the most inaccurate full-size gun I've ever shot. I later traded it in on a Glock 30 and I think I got $75 for it.
Worst ever purchase..... Walther PK380. Bought new and you could not go through a full magazine of ammo without having several FTE's. Thought maybe it was a wear-in issue so I kept feeding the thing more ammo. Somewhere around 1500 rounds the slide started to get loose on the frame and it still had FTE issues. JUNK!!!!!
KelTec PF9 simply because of the controllability. I have a couple friends that don't mind it but I just don't have the grip to control it. I got a G26 and it's twice as heavy but I can shoot it so much better.