So what did she want to tell him? Not the truth, just that he is an asshole, and to give him a check for four thousand dollars, in case he wants to get an apartment. "I feel like I'm on a train in Europe," Sean says, "And you're a little German man, and I'm me. And we're sitting across from each other, and we're talking. But neither of us really understands the other one." Cathy feels that way, too, but her performance is as much about the crazy people in her life as it is about her personal feelings; without the chaos of her brother and her husband, without things to fix and clean and click her tongue over, she wouldn't really exist at all.
Cathy tells her brother, "I understand that you love shocking people, and you think living like this is a good idea right now." What Cathy means to say to her brother is that if he can't learn German than she'll try to speak English, because it's the first day of summer in Minneapolis and she needs to know that her brother knows that he is known. What Cathy means to say to her brother is that he's very much more than a stain on the couch, and that it is a fierce pain because he thinks of himself that way. What Cathy means to say to her brother is that she and her husband are sitting across from each other on a train, and that nobody understands each other. What Cathy means to tell her brother is that she has Stage IV melanoma. But she can't do those things, so she gives him a check.
"I'll give it to the Salvation Army!" Sean swears, and Cathy lunges across the fast food table, and they scuffle loudly, upsetting the other customers, who haven't seen a patrician teacher fistfight a homeless man in a very long time, possibly ever. She begs him not to give it to the Salvation Army, not because she isn't charitable but because he's still not listening. "You want me to have it as long as I do what you want me to do." That's true, in its way, but because she can't tell him the truth of her life, he doesn't know that what she wants is what she says she wants, in English and not quietly: "I want you to be happy."
Sean only hears German. "No, you want to be happy and you think this'll do it for you... I'm freaking ecstatic. I wish you knew what that felt like." Ecstatic, in the Diogenes-holy madman way, he means. And in the regular way, too. Meaning, of course, that his sister is not happy. If she was happy, she would have spent the last year thinking about something other than replacing her punch-stained couch. This also is a fierce pain, because Sean is so about rejecting the material world that he might as well be speaking German, because he doesn't understand that for Cathy talking about the material world is the only way to be honest without giving everything away. That Cathy is never talking about the material world.