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Mel Gibson is nothing if not a complex guy. At Spike TV's Guys Choice Awards on Saturday night, the beleaguered A-lister was a good sport when Brad Pitt yanked his chain over his allegedly tirade-laden 2006 DUI arrest.

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"Thanks, sugar t--s," Pitt zinged after Gibson inducted "Fight Club" into the Guy Movie Hall of Fame. The two later posed together backstage.

But says Mel's sense of humor was nowhere to be found the next day during services at his (as in, he built it) Holy Family Chapel in Agoura Hills, Calif.

The Catholicism-devoted Oscar winner supposedly caused a "huge scene" as he "chastised his fellow churchgoers" over their purported whispering about his private life.

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"[His] holier-than-thou world is falling apart around him," maintains a source. "All these years he's been preaching the good holy word, and now that the wizard's curtain has been pulled back, we find that Mel hasn't been practicing what he preaches."

Gibson, who hit "The Tonight Show" last week to confirm reports that girlfriend Oksana Grigorieva is expecting his eighth offspring (he has seven kids with estranged wife Robyn, whom he split with three years ago after more than a quarter-century of marriage), "got up on his stage -- the altar -- and went off," alleges the spy, who claims he "paced back and forth, furiously telling the congregation that he would not stand by and be judged and scrutinized."

The insider adds that he "tried to intimidate the parishioners by staring at everyone with his angry eyes. Mel even threatened to shut down the church if people kept gossiping about him."

But when we contacted Gibson's spokesman for comment on the so-called rant, he dismissed the accusations.

"There was no 'chastising' that we have confirmed," his rep tells us.

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Meanwhile, in less fire-and-brimstone-y tongue-lashing talk, staffers working on NBC's "I'm a Celebrity . . . Get Me Out of Here!" must be wondering what horrible crime they committed in a past life to be stuck kowtowing to a hissy fit-pitching pack of Z-listers.

Just in time for the show's Monday night premiere, there are whispers galore that after a single day of shooting in the jungles of Costa Rica, contestants Spencer Pratt and Heidi Montag were ready to toss in the proverbial towel because it wasn't made of Egyptian cotton and hung in a luxury suite.

"They wanted to be treated like stars," a snitch tells Ryan Seacrest (via E! News). "[Spencer] literally thought he and Heidi were staying in a Four Seasons, working out and getting a tan."

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After storming off the show twice, the unrepentant self-promoters agreed to stick around.

"If there weren't cameras and it wasn't on NBC, I would already have quit," Spencer huffs to People magazine. "But this is my chance to promote my music, and my wife's music, so I would walk on coals and battle an alligator right now."

Funnily enough, those are two things we'd rather do than be subjected to a second viewing of Pratt's brand new rap video for his ingeniously titled ditty, "I'm a Celebrity" (warning: do not click without ear and eye protection in place -- we're not kidding).

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Also said to be something of a high-maintenance nightmare is fellow contestant Stephen Baldwin.

The reports the born-again actor "flew into a rage" over taking a required physical for the televised fiasco, hollering, "Why would I take a physical? I'm in perfect shape."

All that anger supposedly sent his blood pressure skyrocketing, a situation that was probably exacerbated when the airline lost his luggage, which caused him to once again hit the roof.

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