Pennywise the Dancing Clown
As a clown, Pennywise is supposed to be jovial and happy. However, ironically, he is a violent and demonic clown who kills people - particularly little children.
Pennywise's Red Balloons
Red Balloons, which are a staple of clowns kits, are typically used for good and very happy purposes. Pennywise uses the ballons for a very different, ironic purpose. Instead of using them for good as readers would expect, Pennywise uses the balloons to instill fear into people - particularly members of the Losers club.
The Librarian
Part of a librarian's job description is to encourage members of the town their library serves to learn and read more. The librarian in the book, however, does the opposite, subverting readers expectations. Instead, of encouraging curiosity, the librarian in the book chastises the boy for wanting to learn - and read - more.
The Rabbi
The Rabbi in the book does the opposite of what audiences would expect him to do: instead of wanting to teach and help his son, he acts coldly and dismisses him.
Pennywise
The most menacing and unsettling person in the novel is arguably not Pennywise (who murders children) but Beverly's father, who treats her horribly and possibly rapes her.
