For me, I suppose it was a Charter Arms Explorer II pistol that I bought
way back when I was a Border Patrol Agent in Calexico, CA. I got it at the Yellowmart
in El Centro, CA (that was my go to store for guns & ammo, camping gear, hiking
stuff and fishing tackle. The pistol was both the worst and
the most disappointing for me of any guns I have ever owned. I thought I
was buying a pistol that would be lots of fun, it sure looked cool.
Instead it had lots of jams no matter what brand or type of 22 LR ammo I
used in it and I tried plenty. Some other folks had better luck with
theirs but that model pistol became know in the firearms community as a
Jam-o-matic; so, I guess plenty of others besides me had their share of
problems with it. Mine certainly lived up to its oft used nickname.
My next was another 22, the Smith & Wesson 22A-1. Let me just say, I considered it a total cheaply made piece of junk. That was due to lots of jams (again with many different brands & types of 22 LR) and seeming lack of quality parts and those parts were obviously lacking before I ever shot it. The white nylon buffer, of which they gave three (3) in the box, was a surefire indicator that those parts were not built to last so when the buffers for it run out of stock - and you need another due to yours wearing out - the gun will become useless. Then there was the mag release that almost required the strength of Hercules to release the magazine; that wound up being a problem only with one of the two mags that came with the pistol. So, it probably was not a mag release problem but likely a faulty magazine. I actually had to hit a brass punch with a hammer to get the mag release to go in and then pry the one mag out of the mag well. The next problematic thing was the take-down release. Even the manual said it may be difficult to depress - so S&W manufactured this pistol knowing that would be a pain in the users neck. Next was a bent recoil spring when I took it apart for its initial cleaning before firing it. Now back to that nylon buffer, it was part of the recoil spring & rod assembly. The one in the gun had evident stress fractures in it when I first examined it out of the box. Finally when I looked over the recoil spring again, I counted 15 coils. In the manual a picture of the recoil spring showed one with 13 coils. I guess that something was stressed too much, thus those stress fractures and thus the bent recoil spring, I imagine the extra coils could have caused the stress. My initial impressions of this pistol are here.
Even my RG26 pistol(s), I think, were better made than the two above even though each of the RGs were each just another Jam-o-matic but I will not classify them as the worst or most disappointing - and they were pretty terrible. If you are wondering why I bought two, it was because the RG26 was my first pistol. I eventually took it apart, destroyed the parts, and disposed of the parts. Many years later I bought one at an auction due to nostalgia and nothing more; that wore off soon enough and I sold the second one here in TX.
The third and final of the guns that were the worst and disappointed me the most was a stainless steel Ruger Mini-14 with synthetic stock. I bought it new. When I cleaned it before shooting it, I noticed lots of machining marks on surfaces in the receiver and a bunch of sloppy welds. When I shot it, I could not hit paper at 25 or 50 yards with most shots, no matter what type or weight of 223 ammo I tried with it. On one target, I think I hit it five times probably out of around 100 shots. I had a few jams with it too as it was not extracting or ejecting properly. Then I needed something to whack the bolt handle to open it - that happened a couple or few times. That gun was an utterly dreadful disappointment to me and its performance was extremely lacking to say the least. It's not like I was unfamiliar with Mini 14s and somehow was causing these issues myself. I had been shooting a bunch of them at work and thought they were good to go so I bought it. I have shot plenty of Mini 14s both before and since buying that one and never had similar problems with any of those others. I even took it apart and cleaned it again, probably as good as I had ever cleaned any gun, and while it worked a bit better, most of the issue prevailed and it still shot like shaite. Ruger told me to send it in but I decided I just did not want it even if they worked on it and got it right. So, I sold it instead (and was very forthright about the problems). The buyer got it and loved it. This is the feedback he left me, he also contacted me later to tell me it shot just fine:
"Highly recommend this seller, Well packaged, shipped promptly, great communication, rifle accurately described, photos accurately showed the condition of the rifle. Very Pleased Geat Job!!!! A+A+A+A+"