I'd say most westerns. They were the "true grit of America" when I was a kid....gunfights, native uprisings, range wars, cattle rustlers, the hoosegow, the saloon, bank robbers, stampedes....all that. It was true-blooded, true-grit America as I heard it.
Then I read some actual real history and found out that almost NONE of it was even close to being true, aside from some names and a few notorious events and places. Even "cowboy hats", as we know them, were mostly a fabrication of movies. I was shocked to find out that the "saloon girls" were probably prostitutes and that many of them carried diseases. That's why they went upstairs with the guys. Bison were not hunted so much as slaughtered in order to starve the natives.
Now, I'd take some convincing to even think about seeing a western; can't stand them now. This would pertain to almost all westerns, the further back you go, the worse they get.
That dull looking, slope shouldered, badly dressed guy was the notorious Billy the Kid. He looked much better in movies and TV.