They were at the missionary meeting, and Mrs. Merriweather had made some underhanded and very rude remarks about Atticus defending Tom Robinson in the trial. Here they are, sitting in Atticus's very house, and Mrs. Merriweather has the audacity to say,
"there are some good but misguided people in this town...who think they're doing right...but all they did was stir 'em up."
She is referring to Atticus, who did the right thing to defend Tom Robinson, and how in doing so, it really made all of the black people hopeful, and then when the guilty verdict came down, they were upset with it. She goes on to say that her own servant, Sophy, was "sulky" and "dissatisfied" because of the result of the trial, and that she had wanted to fire her because of it. At this point, Miss Maudie interjects icily, "His food doesn't stick going down, does it?" meaning, Atticus's food that at that very moment Mrs. Merriweather was eating. Miss Maudie was saying that if Atticus bothers you so much, if what he did in helping Tom Robinson-and hence making your slaves unhappy and not as good servants-was so awful to you, why are you sitting in his house and eating his food? Wouldn't you be so disgusted that you wouldn't want to eat his food? Wouldn't it stick a little as it went down because you were so disgusted with him? It pointed out Mrs. Merriweather's hypocrisy; she was bad-mouthing the very person who was helping to make her comfortable at that moment, and didn't even have the guts to mention his name out loud, but instead gave a side-handed insult. It was like spitting on Atticus's front door and then demanding he feed her.
Alexandra, who had been very offended by Mrs. Merriweather's remark, was relieved that Miss Maudie had stepped in, and with one quick comment, pointed out Mrs. Merriweather's rudeness and vindicated Atticus in one fell swoop. As hostess of the party, and as sister to Atticus, she was grateful for the help in putting Merriweather in her place.