In "A Christmas Carol", what reason does Scrooge give for not joining his nephew at Christmas?

Of course, Scrooge first utters his famous "Bah, humbug!"  Then he asks his nephew, "What right have you to be merry?  What reason have you to be merry?  You're poor enough."

To this the nephew counters, "What right have you to be dismal? What reason do you have to be morose? You're rich enough."  Scrooge retorts that he needs to be morose because he lives in a "world of fools."  Scrooge continues,

If I could work my will...every idiot who goes about with 'Merry Christmas' on his lips, should be boiled with his own pudding, and buried with a stake of holly through his heart.  He should!

The nephew is shocked by Scrooge's coldness, but Scrooge tells his nephew to keep Christmas in his own way, and he will keep Christmas in his.