Every day will become April Fool's when die-hard clowns put these tricks into play. Among the comic goodies: replacing the fruit juice with colored water, preparing peanut butter and "worms" (really spaghetti), switching one person's clothes with another's so they'll both feel like "misfits," and leaving phony messages on the answering machine. (That "Mr. Wolfe" or "Mr. Lyons" called from the zoo is a good one.) With lots of school scams, body basics (like a scary "severed finger"), bathroom booby traps, and other forms of psychological warfare, the tomfoolery will last all year.