Can you write a fictional book about real celebrities?

Roman à Clef
Roman à clef (pronounced roh-máhn a clay) is French for "novel with a key." It's a novel in which actual events are given a superficial fictional mask; but, with the "key," can be read as a more or less faithful account of true events. They're often used to report scandals while avoiding charges of libel or sedition.
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From the Guide to Literary Terms by Jack Lynch.

Satire as free speech

But major media groups including the Association of American Publishers, the Motion Picture Association of America, and the Cartoon Network have filed a brief supporting the newspaper's case.

"An adverse decision at the Texas Supreme Court would have a chilling effect on the use of satire in the media," says James Hemphill, lead attorney for the Observer. "Even the specter of having to go to trial and incur the expense of defending political speech is enough to chill that speech."

When the Observer first ran its piece, Isaacks and Whitten were deluged by angry letters and even calls for their resignation. The two officials sued the paper for libel.

Both the trial court and the Texas Court of Appeals agreed with Isaacks' and Whitten's view that satire is in the eye of the beholder. "Satire is not protected under the First Amendment if it fails to make clear to its readers that it is not conveying actual facts," the appeals court wrote.

Like say I wanted to write a book about A wild gay love triangle between George Bush, Dick Cheney, and "Miss Beazley" the Bush's pet Scottish terrier. Could I do that? What could happen to me if I did that?