What does Scrooge feel when he sees his nephew Fred and his friends discussing him?

This scene comes during the time when the Ghost of Christmas Present is escorting Scrooge. At this time, Scrooge is just beginning to feel transformed by the experiences the  spirits show him, so as usual, he resents and dismisses what the guests at Fred's gathering have to say about him—at first. As we've seen in the beginning of the story, Scrooge constantly rebuffs his nephew's attempts to establish a warm relationship, partly because he sees Fred as frivolous, but also, very likely, because Fred's likeness to his mother, Scrooge's beloved sister Fan, brings up painful memories Scrooge does not want to confront.
But, during the course of his observation of the party, he so far forgets himself as to try and participate in the party games (which, of course, he can't, because no one can see either him or the spirit), and when he's revealed to be the butt of a joke answer, his feelings are not what he thought they would be. Suddenly, the fact that these people see him as a bitter, angry, unkind man evokes a different kind of reaction. He's not ready, yet, to acknowledge that he must change for his own spiritual salvation—but the seeds are being planted for that transformation.