Yo, It's Captain America, Y'all

The trailers for summer movies are out.  I just caught one for Captain America: The First Avenger.  As you can see, it's an origin story, set during WWII:



This is a $140 million film.  No expense has been spared to get the look right.  Yet, when our hero is fighting in an alley, he says "I could do this all day." It takes me right out of the movie.  Why does the screenwriter (and everyone else down the line) assume because a phrase (usually rendered "I can do this all day") has been around for a while, it's been around forever?

I suppose someone several generations ago could have put those words together, but it's a specific phrase, not something generic, and I've never heard, seen or read of anyone uttering it back in the 1940s.  He might as well have called his assailant a be-otch.



PS  An even more egregious example of anachronistic dialogue is in the recent HBO miniseries Mildred Pierce.  It's the opening night of Mildred's chicken and waffles restaurant, and it's going well.  Almost too well.  Back in the kitchen, a harried Mildred hardly has time to perform all her tasks.  She notes "I'm waiting on some waffles." Well that would explain the slow service, wouldn't it?