A lot of folks seem to be going off the deep end lately. Moammar Gadhafi claims the people of Libya love him, and he’s prepared to kill them until they agree. Charlie Sheen believes his fingertips touch magic and that the world looks on him as “a winner.” Tom Shadyac, who directed “Bruce Almighty,” is now reborn as Tom Almighty. A television preacher named Rob Bell has inflamed his followers by warning that evangelicals alone don’t have the ticket to heaven.

And I won’t even go into the latest on Lindsay Lohan or Mel Gibson.

At what point does self-destructive behavior become mental illness? Every shrink has an opinion on this, and Dr. Drew Pinsky expresses his almost hourly on TV. I’d argue that delusional people have at least this in common: They’re certain that they are right.

Sheen proclaims he’s such a superstar that CBS will crumble without him and that movie offers are pouring in. “Get real,” advises Bill Maher on his show. “You’re in a mediocre comedy called ‘Two and a Half Men,’ and if there’s no ninth season, art won’t die.”

Gadhafi tells the world that he’s not a wuss like the leaders of Tunis or Egypt, who were voted off the island. Not only does he have a better wardrobe but, if things get tough, he will call up the security guards who handled the Oscar show.

Tom Shadyac opens his self-financed doc titled “I Am” by proclaiming that he’s lost his mind. That’s why he abandoned his burgeoning career directing hits like “Ace Ventura” and “Bruce Almighty” plus his opulent estate and private jet to move into a trailer park.

It was a bike-riding accident that triggered Shadyac’s voyage of self-discovery. The concussion he sustained brought on a siege of depression that in turn led him to conclude that “my life was a waste.”

In fairness, Shadyac’s film is not a wild-eyed plunge into spirituality. Instead, “I Am” represents a thoughtful review of scientific research suggesting that man is instinctively cooperative, not competitive, and that our destiny will depend upon this recognition of interconnectivity.

To Shadyac, the heart, not the brain, is our true boss, and mental illness is the result of “the mindless accumulation of possessions.”

Shadyac now devotes much of his time to mentoring young people on their personal journey, and the kids are clearly in need. A remarkable proportion of teenagers and pre-teens are on serious medication, and a new federal study suggests one possible cause: There’s a significant drop in sexual activity over the last 10 years among the 15-24 age group. This would help explain the causes of cosmic depression.

For the evangelical community, on the other hand, the ultimate downer was delivered by Bell, a Christian TV star from Michigan. In a new book, Bell denounces the dogma that “a few select Christians will spend forever in a peaceful joyous place called heaven while the rest of humanity spends forever in torment and punishment.”

A chorus of Christians promptly thundered that Bell had gone off the deep end — that they know all about heaven and have exclusive tickets to it.

Against all this background noise, a touching show business memoir about depression titled “Haywire” was re-published last week. Written in 1977 by Brooke Hayward, the book relates the saga of a beautiful and gifted family whose members were bent on ruin.

Leland Hayward was a top agent and producer who was married to actress Margaret Sullavan. Living a life of pure glitter, their best friends were the Fondas, Jimmy Stewart and Truman Capote. Yet the family story is one of divorce, breakdowns and suicides. When Brooke first decided to write her memoir, one of her ex-husbands, Dennis Hopper, threatened to sue her.

So does anyone really know where egomania and sociopathy end and mental illness begins? Some public figures might have survived more easily in another era. Sheen could have been a folk hero in the Easy Rider moment of Hopper, McQueen and Mitchum. Shadyac would have flourished in the 19th century communal universe of Charles Fourier and Henry David Thoreau. Gadhafi might have been a heroic pirate in the Caribbean, putting Johhny Depp to shame.

But I don’t know about Bell. Claiming you know your way around heaven has always been a ticket to disaster.