There are four short stories in the book, the first one illustrates why Henry is so horrid. Henry has a little brother known as Perfect Peter. Peter says "please" and "thank you", helps make dinner, and loves vegetables. One day, Henry wonders what would happen if he were perfect. His experiment in perfection drives his perfect brother into horrid behavior. Perfectly horrid!
In the third story, Henry and his frenemy, Moody Margaret, fight over who gets to be Captain Hook, make Perfect Peter walk the plank 14 times, create a huge mess making glop and dare each other to taste it before giving some to the unsuspecting Peter.
There are dozens of books in this series. The illustrator, Tony Ross's drawings remind me a bit of Quentin Blake's drawing for the Roald Dahl books. The Sonoma County Library has three copies and many of the sequels. The AR is 3.3.