Usually, the historical inaccuracies.
Vikings had a lot of them.
Or worse... Spartacus.
Well, most movies do.
I like the fact that in the movies slaves with zero education have a richer vocabulary than many people from the present.
Like... you know what I'm saying... like?
Also, how could Al Bundy afford a big house with an unemployed wife and 2 kids?
I was watching Terms of Endearment and I remember that the college professor had a crappy smaller house and the family had money problem.
Do shoe salesmen make more money than college professors in USA?
Did the American Indians have horses?
I think not!