What's the Significance of Frank James (James Brolin) At the End?

Frank James was a notorious bank robber and murderer. Not surprising the outspoken Mattie would put him in place like that.

The way I took the scene was that she thought it was rude that he didn't stand up.

The two men are Cole Younger and Frank James who did run a real Wild West show in the early 1900's. Cole Younger was a bandit, Frank James was by all accounts worse than his brother and a ruthless killer.

Younger did go to prison, more for association with the gang than any real crimes. Frank James never paid for his crimes, in her mind.

In the book some of the characters do talk about the James brothers and they explore Rooster's criminal past.

It's all simply a case of manners. Younger stands for Mattie, whilst James stays seated. Mattie then proceeds to castigate him, when taking her leave. We learn during the film, that young or older she never holds her tongue.🐭

Cole Younger and Frank James (brother of Jesse James) were actually cousins and active members of the James Gang. Also, during the movie, Rooster talks about fighting in the Civil War under Captain Quantrill in Kansas and Missouri. Both James brothers, along with Younger, also were members of Quantrill's border raiders, so most likely Cole Younger and Frank James knew Rooster from the Civil War days and reunited for the Wild West show.

It was rude of him not to stand, but she didn't have to be so nasty. Just another reminder why she never had a significant other

I doubt Mattie could have cared less if a man stood for her or not, that's her nature. In my view she knew exactly who who he was and that's the reason for her comment.

Here's the deal with the ending. In the book, Mattie Ross went to either see Rooster at this wild west show or go pick up his body (I don't remember which). Anyway, she has an internal monologue about meeting Cole Younger and Frank James. She mentions that she respected Cole Younger because he had served time in prison for his crimes. However, she thought Frank James was white trash because he was a bank robber who evaded justice. I don't remember if she actually told him that in the book. I haven't read it since the 1990s. But the ending of the 2010 movie doesn't provide any context for her statement nor does it really have any place within the narrative of the film.

I'm planning on reading the book again in the near future, because there were quite a few things in the newer movie that seemed like they were changed.