An old saw about Hollywood has it that if you scrape away the phoney tinsel, you'll find the real tinsel underneath. On the evidence of the would-be hiss-and-tell exposÇ at hand, much the same could be said of Donald Trump, the casino real-estate operator who's now adrift in a sea of financial woes. By the author's evenhanded, knowledgable account, in fact, Trump is a decidedly dull boy whose life story could as easily have been subtitled ``The Banality of Narcissism.'' The son of a top gaming-industry executive, O'Donnell (now 36) grew up in the slot-machine business. A sometime protÇgÇ of Steve Wynn, he signed on with The Donald's organization in 1987. As chief operating officer at Trump Plaza, O'Donnell was in almost daily contact with his boss. If familiarity did not breed contempt, it eventually led to distaste. Trump at work emerges here as a cocksure boor who pays precious little attention to detail and pins the blame for his own misjudgments on subordinates. While he seems surprisingly dumb when it comes to weighing a deal's downside risks against its potential rewards, he apparently suffers from near- terminal overconfidence. As O'Donnell makes clear, however, his empire was built on an abiding faith in rising property values, an assumption that came a cropper shortly after the Taj Mahal's botched opening. And Trump at play with his yacht, helicopter, and other trophies is an equally unappealing eminence. A lover of gossip, The Donald has a phobia about germs, which makes him reluctant to shake hands with high-rolling customers or mingle with the celebs he adores and caters to. Nor does the abstemious Trump have a talent for extramarital flings. A long-running, oddly joyous affair with Marla Maples cost him his marriage to Ivana--and a good deal more. At any rate, O'Donnel quit Trump cold about a year ago. Now employed at Merv Griffith's Resorts Casino Hotel, he's watched from afar as Trump's sagging fortunes have attested to the truth of Hardy's contention that character is fate. An insider's saavy appraisal of a lad who lierally grew too big for his britches; no real surprises or new dirt for attentive readers of tabloid and business news, but a slick piece of work that will almost surely attract attention.