Dill is still mad at his Aunt Rachel, who is angry at him for joining Jem and Scout at the trial without permission. He is also upset with the outcome of the trial and the treatment Tom received from the prosecutor and the jury. He decides he is going to be a clown when he grows up so he can laugh at people all day long. Jem explains to Dill that clowns are sad, and that people laugh at them instead. Dill will become a new kind of clown, he says, one that will laugh at people instead of them laughing at him.
Dill is a very unhappy young boy at the moment. He has just run away from home because of his indifferent parents and his abnormal home life; he doesn't get along with Aunt Rachel, who he claims should be "ridin' broomsticks"; and he has little faith in people after watching the innocent Tom mistreated by the Maycomb jury. Dill just wants to be happy, and being a clown seems like a good way to stay that way.
In Chapter Twenty-two of Harper Lee's To Kill a Mockingbird, Dill decides that he will be a non-traditional clown. He announces that he will laugh at people. Jem reminds him that clowns are usually sad, but Dill argues that he is going to be a new kind of clown that simply laughs at other people.
'I think I'll be a clown when I get grown,' said Dill...'Yes sir, a clown,' he said. 'There ain't one thing in this world I can do about folks except laugh, so I'm gonna join the circus an laugh my head off.'
'You got it backwards, Dill,' said Jem. 'Clowns are sad, it's folks that laugh at them.'
'Well I'm gonna be a new kind of clown. I'm gonna stand in the middle of the ring and laugh at the folks...'
In support of his statement, Dill points to Miss Stephanie and Miss Rachel who are in the middle of a gossiping frenzy, and Scout believes that Dill's point is well-taken.
Dill may be saying this to attempt to cope with the ugliness in the world. Tom Robinson has been found guilty, and it is in this part of the story that we learn that Bob Ewell has spit in Atticus' face. Laughing at the foolishness of others seems to be the only way that Dill can find to cope.
However, in the light of the gossip taking place, eNotes states that Dill's character is based on Truman Capote (who was made fun of). Dill's plan to become a clown may reflect a need to be his own person and make people happy. Seemingly unable to do both (with Capote in mind), Lee may use the character of Dill to address the difficulty of measuring up to other people's standards—as unfair as that expectation is.
[Dill] plans to become a clown and laugh at people rather than having them laugh at him.
Dill career choice to be a new kind of clown is showing a great sign of maturity. Dill says he wants to be a clown that laughs at people instead of people laughing at him. This means that Dill wants to laugh at people (society) because they are being so dumb in the Tom Robinson court case.