A great gig for the father of dysfunctional ditties

He’s sung of the relationship advantages of tragic demise, of dads bitterly jealous of newborn sons, of disenchanted daughters, of lovers in search of each other’s perfect therapist and, in his biggest hit, of a dead skunk in the middle of the road.

So who better to create the music for Judd Apatow’s new comedy of dysfunctional love born of a one-night stand than Loudon Wainwright III?

The veteran singer-songwriter is 60, old enough to be Apatow’s father. That’s a fantasy undoubtedly entertained somewhere along the line by the loose-cannon creator of “Knocked Up” and “The 40-Year-Old Virgin” and short-lived TV shows “Freaks and Geeks” and “Undeclared.” Like most of the songs Wainwright has recorded since the early ‘70s, they’re rife with relatives and friends you wouldn’t wish on an enemy. Well, Bin Laden, maybe.

“If I had never been exposed to Loudon, I would probably just be writing fantastic [male anatomy] jokes, but nothing more,” Apatow, 39, says in the notes for Wainwright’s new album, “Strange Weirdos,” subtitled “music from and inspired by the film ‘Knocked Up.’ ” “Loudon’s work ... is a powerful reminder to me that I must always be honest, funny and true to myself.”

Having turned Wainwright into a TV dad six years ago in the Fox series “Undeclared,” Apatow returned to him this time not just to write songs but also to compose the score, with help from another Wainwright acolyte, Joe Henry.

“Any excuse to stay at home in my pajamas and get paid for it is OK with me,” Wainwright said recently. “Running around with a guitar from town to town gets less and less fun the older I get.”

Yet it was at just such an occasion, when Wainwright was playing an L.A. club, where Apatow heard him sing “Grey in L.A.” and thought it would be perfect for the film hatching in his brain at the time. The song helps set a skewered tone for “Knocked Up” as Wainwright rails against the Southland’s incessantly sunny weather and Hollywood-centric mind-set:

Brad Grey’s in L.A.

Yeah OK I should stay here

There’s no place that’s better I know

For a wannabe star stuck in a car

On a freeway with nowhere to go

With his first bona-fide film score to his credit, Wainwright, increasingly famous in recent years as the real-life dad of singer-songwriters Rufus and Martha, can now entertain his own fantasy of wrestling with fellow singer-songwriter-turned-composer Randy Newman over an Oscar for best original score.

“Yeah,” he says, “I’m ready to duke it out with him.”

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