Dave on Demand: Your candidate here -

Whoever came up with the phrase "No one is irreplaceable" probably worked in the TV business.

Charlie Sheen has an acrimonious parting of the ways with Two and a Half Men? Steve Carell opts out of The Office? The shows will go on.

But the industry faces a new challenge: How do you replace someone who defects from a reality show? I submit that you solve it the same way: stunt casting.

MTV's Jersey Shore took two major hits this week as first Vinny and then the Situation walked out on the taping of the fifth season in Seaside Heights.

We got ourselves a serious Guido shortage here, folks.

Although he's more charismatic, the Situation should be easy to duplicate. The thick-accented dolt who thinks he's God's gift to women has been a stock character on the tube for decades. Think John Travolta on Welcome Back, Kotter, Tony Danza on Taxi, or Joey Lawrence on Blossom. Matt LeBlanc has made an entire career out of playing guys like the Situation.

I nominate Mark Salling, who plays Puck on Glee. Coat him in tanning oil and he could slip into the role tomorrow.

Who will take on the role of the eternal wingman Vinny? Danny DeVito has all the tangibles - most important, a high tolerance for alcohol - but he's too old. Howard Stern sidekick Artie Lange might suit, but he's undependable.

I'm going with Bobby Moynihan, famous for dressing in drag to impersonate Snooki on Saturday Night Live. He's already got the attitude and the accent down.

And if (heaven forbid) Snooki should ever leave the show, you have an understudy already pruning up in the hot tub.

Easy pickings. Circling back to Charlie Sheen for a moment, it was announced this week that he will be the target, er, guest of honor for one of Comedy Central's signature roasts.

Programming note: it is scheduled to air on Sept. 19 at 9 p.m., which puts it squarely up against the season debut of Two and Half Men on CBS. What are the chances of that?

These roasts are more like eviscerations, as one insult comic after another takes to the podium to savage the man of the hour. But playing This Is Your Life with Sheen? That's like shooting carp in a teacup.

Learning the language. Chris Colfer, who plays Kurt on Glee, recently tweeted: "My mom JUST told me that my first word was OPRAH!!!"

I'm told that my first word was Urkel. That probably explains a lot.

Thanks for reminding me. ABC News has announced that it is hiring Elizabeth Smart as a contributor. According to a network spokesman, Smart, 23, will be called upon "when there are missing children or missing-person cases in the news."

Smart became a national name when she was kidnapped at 14 from her home in Utah. She was rescued nine months later.

Ignoring for a moment the fact that this is a macabre hire, at least it's not a very demanding gig. It's like being the official justice of the peace for The Bachelor: Chances are you'll be called upon rarely.

Time off for good behavior. Weeds, one of my hot-weather favorites, returned this week. Three years have elapsed and Nancy, just paroled from federal prison in Danbury, Conn., is living in a seedy halfway house in Manhattan.

Word of her release soon reaches her exiled clan in Copenhagen, who resolve to join her.

That leads to the sort of acute line that makes me so fond of this show, as Andy says, "We're going to America . . . land of hot sauce and catastrophic wealth imbalance."