Oh where to begin?
Watching Season 3 or 4 of 24 and Jack Bauer is in a shoot out with some terrorists. He is armed with a handgun, they are armed with Ak47s. Now he is able to hide for cover behind a car while it is completely sprayed with bullets.
Then leap up and tag guys all over and even gets hit in the chest by a few rounds.
Luckily he was wearing standard Type II body armor and the 7.62x39 just made him winded instead of punching through him.
Reading the book Hannibal the bad guys have a Dragunov sniper rifle in oh like 1948 or 1950. Funny the gun wasn't even invented till the late 50s and didn't see service until the 60s.
Other bad movie stuff:
Hiding for cover behind a car from rifles (M16s,M4,AKs, and full on M60s, M240s and HK91/G3s)
Ducking down when bullets are being shot at you while driving. As if the dash, or trunk will stop rifle rounds from hitting you. Extra points for ducking when a guy in a helicopter is shooting at you.
Silencers that are so quiet you don't even hear the action of the gun clacking.
Machine guns that shoot way longer than their mag capacity. Nothing like watching some guy shoot full auto for 10 15 seconds without a mag change.
Every time the hero can some how magically duck/dodge/dip/dive/dodge a guy with a gun pointed at him and get in close enough to disarm them easily.
Guns going off when dropped.
Pump shotguns repeatedly racked for no reason.
Multiple clicking noises after a gun is empty but the bad guy isn't dead. Click click click.
Hero is using only a handgun, kills multiple baddies and never picks up more ammo or even a new weapon.
Bullet proof armor always works except against 'cop killer bullets' and people are always hit in the chest and just fall down. But are able to get up and keep going.
Gun shots to the shoulder allow the hero to be wounded but still somehow lets them climb that building to beat the bad guys.
Gun fights where no one takes cover and just stands or crouches there while everyone gets shot and dies.
Gun fights in doors and seconds later the hero or villain whispers something important and everyone in the room can hear just fine.
Hand someone a gun, that has never shot before and not only do they know how to use it, they can easily kill people with it and are an expert with it.
If a person isn't using a 1911, Beretta 92FS or an M16 varient they are a bad guy. Cause good guys would never use an AK47, HK, Steyr, etc.
Bullets can set gas on fire with one shot. Especially bullets aimed at a diesel truck tank.
Bullets always ricochet.
Bullets also always spark and explode.
A handgun can take down anything from cars, trucks and airplanes. All it needs is one good shot.
If you run from a helicopter or plane shooting at you, you will get mowed down. Stand still and the bullets will harmlessly pass on both sides of you.
Any western set before 1880 that has gun fights that don't become a cloudy haze in seconds because smokeless gunpowder wasn't widely available until that point.
Bad guys keeping people hostage and at gun point with TOY GUNS, and no one noticing they are fake, until the twist at the end!
Hero gets gut shot and it sets him on his path to kill the guy that gut shot him. When the villain is finally killed he dies immediately from a gut shot.
Not so much a gun error but explosives error. Being able to run away from a grenade or bomb blast going off and the fire not going into the room or tub you jumped in.
No one other than law enforcement or criminals owns guns. The only time a hero etc can find another weapon is from a cop or bad guy. They never own their own, or have non criminal friends that own one.
AK47s that jam after a few rounds and are impossible to fix. I have NEVER ever seen one jam other than a FTE. Pull back the bolt shake it out and go again. As opposed to the movies where the gun is basically a club now because it has some magic jam.
No one ever has a stove pipe, failure to eject, dud round, or failure to feed, unless it is a bad guy or important to the story/action.
WWII German guns always jam. ALWAYS even fresh from the factory etc. The only exception is when an American is using them against Germans.
Gun fights where a gun has been fired a bunch and the hero can just grab it by the barrel and fling it away and their hands are just fine.
Fires hitting an armory or truck loaded with ammunition and it always cooks off and no one is ever hit by any stray bullets or shrapnel cause they ducked.
and finally
Any time a gun shot knocks a person backwards.