Joann Davis, former Warner and HarperCollins editor who has just hung out an agent's shingle, made a quarter-million-dollar sale of a book about the pithy observations of a notable trend tracker's 85-year-old Italian aunt that sounds as if it might have the makings of a new Tuesdays with Morrie. It's called What Zizi Gave Honeyboy, and the author is Gerald Celente of the Trends Research Institute in Rhinebeck, N.Y., whose Trends 2000 Davis had published at Warner. Zizi, from Yonkers, N.Y., is an old-school Italian who thinks things are going to hell in a handbasket and tells Celente so in no uncertain terms. The buyer was Morrow executive editor Mauro DiPreta, who aims to publish probably next spring; he took world rights and audio.