Book excerpt: Knock, knock. Who's there? Someone with sad underwear. Sad underwear? How can that be? When my best friend's mad at me, Everything is sad. Even my underwear. Only Judith Viorst, with the perfect pitch for the trials of childhood that has made her Alexander books modern classics, could create an ode to melancholy unmentionables. But the title poem is just one of the many pleasures in this collection, which bursts with wit and understanding -- and the occasional poignant note. Sure to delight readers of Shel Silverstein and Jack Prelutsky, as well as Viorst's own legions of fans, Sad Underwear is a perfect companion volume to her celebrated If I Were In Charge of the World.