For the second year in a row, Dav Pilkey's potty-humor-loving Captain Underpants graphic novels - "Action! Thrills! Laffs!" - about a couple of rowdy fourth-graders who turn their mean principal into a superhero dressed only in cape and undies while he fights the villainous Dr. Diaper, topped this year's list of kids' books most challenged by parents who are evidently not crazy about the references to pee-pee, boogers, tinkle and barf that their kids, with the usual discerning taste of eight-year-olds, adore. The series, with titles like "Captain Underpants and the Attack of the Talking Toilets," has been much praised for getting otherwise book-wary kids to read. It was cited for "offensive language" and being "unsuited for age group" on the list released this week for National Library Week, part of the American Library Association's 2014 State of America's Libraries report. Runners-up were Toni Morrison's acclaimed early novel The Bluest Eye and Sherman Alexie's The Absolutely True Diary of a Part-Time Indian, cited for offensive language, sexual explicitness, drugs, racism or violence - subjects, ironically, they are in fact addressing, though their detractors don't seem to get that. Next on the list is mommy-porn favorite Fifty Shades of Grey, which has been critically, hilariously lambasted but was cited for other reasons than atrocious writing, and The Hunger Games, cited for "religious viewpoint," not murdering children. Because what makes sense here?