But what is surprising is that it is not number one.
First on the list of the most offensive library books is Dav Pilkey's Captain Underpants books, followed by Sherman Alexie's The Absolutely True Diary of a Part-Time Indian and Jay Asher's Thirteen Reasons Why.
The list was compiled by the American Library Association after their annual study of "challenged books." It consists of books most complained about by parents, educators and other public library goers.
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Some unexpected books also made the list, like Nobel laureate Toni Morrison's "Beloved."
Authors worry that the list will discourage people from reading their books.
"It's pretty exciting to be on a list that frequently features Mark Twin, Harper Lee and Maya Angelou," author Dav Pilkey said. "But I worry that some parents might see this list and discourage their kids from reading Captain Underpants, even though they have not had a chance to read the books themselves."
The association determines who makes the list after going through complaints filed with libraries.
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Last year, they received much more complaints than normal, likely due to people filing them online.
They received 464 complaints in 2012, a 25 percent jump from 2011. It is still much lower than it was in the 80s and 90s, however.
"One reason we think the number went up in 2012 is that we made challenges easier to report by including a portal on our Web page," Barbara M. Jones, director of the OIF, said.
It is not clear how many books were pulled due to the complaints.
When Fifty Shades of Grey was put on the shelves last year, many libraries soon pulled them after deciding that the books were too steamy or poorly written.
Others decided the book series was "semi-pornographic" and "unfit for community standards."
While it seems odd that a children's book topped the list as the most offensive book, many have challenged it over the years because of its "toilet humor and irreverent attitude." But others have praised it for encouraging boys to read.
"I don't see these books as encouraging disrespect for authority. Perhaps they demonstrate the value of questioning authority," Pilkey said. "Some of the authority figures in the Captain Underpants books are villains. They are bullies and they do vicious things."