Operation: Dump the Chump — Barbara Park

CHUMP OF THE YEAR
Poor Oscar Winkle! Ever since his little brother Robert (not-so-affectionately known as the Slobert) showed up, he's specialized in ruining Oscar's life. He even brought Oscar's underwear to school for show-and-tell!

Finally, after seven and a half years of Slobert-style torture, Oscar decides he's had enough and comes up with a wickedly brilliant, top-secret scheme to get the ultimate revenge. It'll take stealth, courage, and determination (not to mention a few whopping lies), but Oscar is persistent. He calls the plan Operation: Dump the Chump, and if he can carry it off without a hitch, he'll have a better present than money could buy -- a Slobert-free summer!