What does Aunt Alexandra say about Walter Cunningham Jr. that makes Scout extremely upset?

In Chapter 23, Atticus is discussing the trial with his children and mentions that one of Walter Cunningham's relatives was on the jury, and he initially voted to acquit Tom Robinson. Before he leaves the room, Atticus explains how the Cunninghams come from a respectable family. Scout makes the comment that as soon as school starts, she's going to invite Walter Cunningham Jr. over for dinner. Aunt Alexandra says, "We'll see about that"...

In Chapter 23, Atticus is discussing the trial with his children and mentions that one of Walter Cunningham's relatives was on the jury, and he initially voted to acquit Tom Robinson. Before he leaves the room, Atticus explains how the Cunninghams come from a respectable family. Scout makes the comment that as soon as school starts, she's going to invite Walter Cunningham Jr. over for dinner. Aunt Alexandra says, "We'll see about that" (Lee 299). Scout looks surprised and asks why not, and Alexandra tells her that the Cunninghams are not their "kind of folks." Alexandra elaborates by commenting that someone can wash Walter and put him in a new suit, but he'll never be like Jem. She also says there is a drinking streak in Walter's family, and Finch women aren't interested in that sort of people.

Scout continues to argue with Aunt Alexandra and asks her again why she cannot play with Walter. Alexandra snaps and says,

"Because--he--is--trash, that's why you can't play with him. I'll not have you around him, picking up his habits and learning Lord-knows-what. You're enough of a problem to your father as it is" (Lee 301).

Fortunately, Jem is there to grab Scout and walk her out of the room before she loses her temper. Alexandra's comments depict her prejudiced feelings towards individuals from the lower-class. Rather than judge Walter on his integrity and character, she views him with contempt because he comes from a poor family. Scout is deeply hurt that her Aunt will not let her play with Walter. Scout learned from her father to treat everybody -- regardless of race or social class -- with respect, which is why she disagrees with Alexandra's views about Walter Cunningham Jr.