Captain Underpants and the Perilous Plot of Professor Poopypants: by Dav Pilkey - old paperback
George and Harold aren't bad kids. They just like to 'liven things up' for everybody. Unfortunately-their thoughtful jokes sometimes get them into a ton of trouble and when Professor Pippy P. Poopypants becomes their new science teacher, well-George and Harold almost cause the entire planet to be taken over by a maniacal-mad-scientist guy in a giant robot suit! Who will stop the perilous plot of Poopypants? This looks like a job for Captain Underpants!