For 10 years I worked weekends and summers for a friend who owned three Gun and Police Gear shops. I even got rated as an assistant instructor and Glock Armorer.
We had an event locally where a late teen type had a gun go off in his backpack in class he had his hand in the back pack and dropped it on the floor as it went off - his court defense was it went off when the pack hit the floor and the other students in the room were divided (as normal) on if it fired before or after it hit the floor.
A couple of the local cops and someone from the DA's office came to the shop to get info and advice before the trial. At the time my friend had one of the same model revolver in stock that was so beat up we were going to strip it for parts to sell to a gunsmith and melt the rest.
So he put blanks in the gun and then we proceeded to drop, throw, kick etc. the gun around, both with the hammer cocked and un-cocked. We kept that up for almost 5 minutes including a circle of 4 guys kicking the cocked gun back and forth across a concrete floor for almost 2 minutes - sort of "revolver soccer". We never got it to go off "by itself".

A week later one of the cops came back in and told us that after he and his partner + the guy from the DA testified to what we did without getting it to go off the kid broke down and confessed: 1. he reached in the back pack and cocked the gun 2. he gripped it with his finger on the trigger intending to pull it out to scare someone "as a joke" 3. as he pulled on it the gun caught on something inside the backpack so he jerked harder - that was when the gun went off because he had his finger on the trigger. And the idiot also said he forgot he had loaded the gun then forgot to unload it when he put it in the backpack for his planned "joke". The judge provided a punch line for his joke - one he was not very happy with.

I know of one type of gun (a semi-auto military rifle) that has a part that when worn badly and slammed hard on something butt or muzzle first will go off. It was the early production runs of that rifle, they corrected the problem. A few models of semi-auto pistols with extremely worn down sears can fire when something hits the cocked hammer very hard. But it is rare and then only in guns that are not inspected or cared for and the sears replaced when that badly worn.
At the shop we once got a high end 22 target pistol from a police confiscation auction* that had deliberately and very carefully had the sear filed down and a lighter than spec recoil spring put in so that when fired it went full auto. Everyone in the shop and about 1/2 dozen local cops came in to play with it in our bullet trap before our gunsmith replaced the two parts. I tried it, with 22 shorts it just sort of vibrated as it fired (it was a "heavy" barrel target model) and kept all the rounds on target at 5 yards. And it emptied the 10 round magazine in just over one second. After fixing it so it was legal again a part timer at the shop bought it and then proceeded to win some competitions at the local gun club.

*The department it was purchased from said the guy they took it from was supposedly a hitman for a local drug gang. But they only got him on felon in possession and possession of an automatic weapon. No known hits/bodies shot with it had ever been found. But the two other charges got him 10-20 years and the state judge ruled they would be served after the Feds were done with him. The Feds tried and convicted him on the same two charges and they also gave him 10-20 Federal time. I doubt he got any time off for good behavior at either prison so he would have done a total of 40 years.

At the shop we had a .32 auto dropped off for evaluation and repair. Only thing the guy said to the clerk who took it in (while the rest of us were at lunch) was "When I shoot it it behaves funny." ???????????? What? didn't fire, jammed, failed to eject or started telling jokes?

I got to be the one to test fire it in our bullet trap. So I get out some .32 ACP, load the magazine, go into the back room to the bullet trap (which also had barrier walls around it), insert the magazine and chamber a round, stick the muzzle in the bullet trap and Brrrrrppppp - full auto. Yes it was a surprise. I guess that qualified as it "behaves funny".
Our gunsmith fixed it and found that "someone" had been filing on the sear and cut coils out of the spring trying to give it a "hair trigger".
When the gun was picked up the guy admitted he had done it himself with a book on gunsmithing he bought. His admission might have had something to do with the fact that two of the part timers at the shop who were standing there when he was questioned were LEOs with their badges hanging on their belts. He was told to get rid of the home gunsmithing book and use our gunsmith. He did.