Some things that belong in the "...Never Mind HOW I Know, I Just Know!" category.
'Spin-cocking' a full size Marlin 336/30A/1895 a-la "The Rifleman" WILL get you smacked in the face by said gun....{N.M.H.I.K., I.J.K!}
Pressing that little silver shiny thing waaaay back inside a Rem 1100 receiver WILL cause it to slam the bolt home, poking a hole in the web of your hand with the extractor....NMHIK, IJK
Loading up your "Pistol-Grip-Only" shotgun with Serious Duty magnum buckshot, then attempting to 'wingshoot' a clay target by swinging shotgun up and pointing as though it had a normal stock on it WILL result in a severely mooshed face, complete with 'Rocky Raccoon' eyes, bloody nose and 'Fat Lips'...NMHIK, IJK
Not moving your hand out of the way fast enough while reloading the US Rifle Cal .30 M1 WILL result in a condition known as "Garand Thumb"...NMHIK, IJK (actually, this is only a rumor, as {so far} I have managed NOT to slam the M1 bolt home on my hand.)
Trying the "Speed Load" on a break-open single-shot shotgun without sufficient slo-mo practice first, WILL result in jamming your thumb into a hot chamber...NMHIK, IJK
A scoped bolt-action .338WinMag rifle has SIGNIFICANTLY more recoil than a similar model scoped .22LR, and if the .338WM is held as loosely as the .22...well an instant membership in the "Half-Moon-Scar-Above-The-Eye Club" is awarded...NMHIK, IJK
Not really 'gun violence' but more like 'gun sneakyness'...The smaller a part that has been removed from a firearm, the more likey it is to run off the table and hide in the carpet, under a cabinet, etc...