It must have been conceived as some sort of cruel joke.

For seven seasons now, the judges of “American Idol” have repeatedly told contestants to steer clear of singing songs by Mariah Carey, ostensibly because the singing competition’s up-and-coming star wannabes could never hope to measure up to one of the great voices of pop music.

So, let’s just say it was a little strange to find Carey as the guest judge on Tuesday night’s show. Because you know what that means: the contestants were allowed to perform an old Mariah song, a new Mariah song, or any other Mariah song of their choosing.

As judge Simon Cowell predicted at the beginning of the show, the night indeed turned out to be lackluster one for the girls because of the unavoidable comparisons between them and the great Carey herself. That didn’t stop Cowell from delivering his usual barbs, however.

“It was a bit like ordering a hamburger and only getting the bun,” Cowell told Brooke White after her performance of “Hero.” “In other words the vital ingredient, the bit in the middle, was missing.”

Ouch.

The other girls — Syesha Mercado, Kristy Lee Cook, and Carly Smithson — emerged without being compared to fast food, but they didn’t get any overwhelming love from the judges.

The remaining three boys, however, put the judges in a festive mood. A leather pants-clad David Archuleta’s performance of “When You Believe” was declared the evening’s benchmark by Cowell, and David Cook’s rock take on “Always Be My Baby” received a standing ovation from judge Randy Jackson.

Later, Jackson likened Jason Castro’s take on “I Don’t Wanna Cry” to “a weird beach luau,” but Paula Abdul said it was a luau that she would “love to be at.” Cowell agreed with Abdul, saying that “the guys completely won the night.”

Oh no he didn’t.  Unfortunately, oh yes he did.

Rocker David Cook bombed on “American Idol” Tuesday night with an unfamiliar song and cocky performance that made it seem like he believed he had already wrapped up the competition.

Cook chose “Innocent,” a song by Canadian alternative rock band Our Lady Peace, to sing on a night when contestants were told to choose music that inspires them. The night’s theme was intended as a preview for “Idol Gives Back,” the show’s charity special that airs on Wednesday.

Cook, wearing a white military-style jacket, strutted around without his signature guitar, finally sauntering through the audience while he sang. But judges Randy Jackson and Simon Cowell were decidedly uninspired, with Cowell calling it “a teensy weensy bit pompous.” Only Paula Abdul liked it.

To make a bad performance even worse — cringe-worthy, in fact – Cook ended it by raising a palm scrawled with the words “give back” up to the cameras. The judges praised him for that move, but Cook already appeared completely deflated after their criticisms of the performance.

It was clearly a rude awakening for Cook, who has become a favorite with the show’s fans in the last few weeks.

Another weak performance was Irish diva Carly Smithson’s take on Queen’s “The Show Must Go On.”

Smithson, who had a stellar run on the show at the beginning of the season, is clearly struggling. Cowell, who called her performance “angry,” said she may even be vulnerable to elimination this week. If that does happen, Smithson would be going home before Kristy Lee Cook, the leggy blonde country singer who has narrowly escaped the hatchet for several weeks running.

Never is “American Idol” better than when seemingly second-rate contestants emerge from the shadows to blow the annointed frontrunners out of the water.

Rocker David Cook has managed to pull that off a few times this season already, most memorably with his rock take on Lionel Richie’s “Hello” before he even made it into the Top 12. Still, the 25-year-old hasn’t garnered anywhere near the attention seen by babyfaced teen David Archuleta or Irish diva Carly Smithson.

But on Tuesday night, Cook may have shed the “dark horse” mantle once and for all. His gutsy transformation of “Billie Jean” into a rock ballad prompted judge Randy Jackson to call him “the most original, the most bold contestant we’ve ever had… dude, you might be the one to win the whole lot.”

Archuleta, on the other hand, got mixed reviews for his performance of “You’re the Voice,” with Simon Cowell telling him it reminded him of a theme park performance.

Still, on the “Idol” forums, Cook lags Archuleta in the number of posts viewers have written about him. After Tuesday’s show, hoever, at least one die-hard “Archie” came out to give Cook a hand:

“He’s showing that my second favorite (him) isn’t too far behind my first (David Archuleta, obviously)”

Keep going, David (Cook). One more week and you just might take over that other David once and for all.