What the Heck Just Happened To My Body is a book for boys about puberty written by Darlene Wade. On the cover of the book is a shirtless boy hitting puberty, with the book's title being in the boy's thought bubble.
Susan gave Greg the book one day when he came back from school, along with a stick of deodorant. Greg thinks his mom gave Rodrick the same book when he was his age, because he claims to have seen it in Rodrick's junk drawer. Immediately after unwrapping the book and deodorant, Greg threw the book away because he didn't want to see the disgusting pictures a second time.
It only appeared in The Ugly Truth. It might be talking about puberty. The book is a representation of children's books which document human sexuality and puberty, most notably It's Perfectly Normal and It's So Amazing, which have been controversial.