What's more controversial than Fifty Shades of Grey? An almost-nude, crime-fighting Captain Underpants, apparently. In 2013, the children's book was named the most frequently challenged book by the American Library Association, for the second year in a row. Captain Underpants beat out the erotic Fifty Shades, along with The Bluest Eye by Toni Morrison and The Absolutely True Diary of a Part-Time Indian by Sherman Alexie.
