There is really only one idea in Kenny Mellman and Bridget Everett’s new show, “Sexercise Live!,” playing through tonight at PICA’s 2008 TBA Festival. And – attention must be paid – it’s a pretty good idea.

It goes something like this: take a slice of recent historical pop culture – the raunchy rap and soul songs of legendary singer Millie Jackson, in this case – rich in ironic potential; mine that material for the most outrageous and colorful gems; and present them in a stripped down, straight-ahead performance that acts as contemporary comment on the material. Hilarity ensues.

That hilarity, of course, comes from the interpretive distance between the original songs (dirty, down-low tunes performed with real intensity by an African-American soul star), and the modern interpretation (flailing theatrics by a trio of white musicians, fronted by a buxom, no-holds-barred blonde with a big voice).

This is a concept that pianist Kenny Mellman – better known as the hard-drinking, keyboard-thrashing half of that legendary duo, Kiki & Herb – has mined before, in revues of music by Grace Jones (“I’ve Got a Bulletproof Heart,” TBA 2005) and, in collaboration with fellow ironic-pop song album showman Neal Medlyn, the R. Kelly songbook (“Kenny Mellman + Neal Medlyn = R. Kelly,” TBA 2006). Medlyn, also a TBA Festival regular, popped up last week in yet another pseudo-serious irony-soaked revuesical, recreating r & b starlet Beyonce’s 2007 DVD, “The Beyonce Experience Live!” He has a cameo in “Sexercise” too, and without giving it away, it is one of the funniest and best-conceived parts of the show.

The “Sexercise” formula is straightforward: Mellman and Everett present selections from the Jackson songbook essentially in concert format, from the diva’s most-celebrated Top 40 hits (“If loving you is wrong, then I don’t wanna be right”) to obscure raunch B-sides (“Girl gotta know she’s a ho”). The formula is also lacking in just about every element to really make the show catch fire – it is unevenly constructed, in dire need of a director’s guiding hand, and too often substitutes manic energy for theatrical magic.

Everett, in her TBA debut, is a kind of chunky Storm Large on steroids, but without the wit: she belts her songs aggressively into a hand mic, shakes her tits with cheery abandon, and grinds her pelvis on front-row male audience members. There’s something special about Everett’s unbridled enthusiasm and her way with a four-letter word, but Mellman’s over aggressive pianism – skidding dangerously close to his much-admired “Herb” persona – and loose musical direction ultimately disappoint.

Near the end of the night, after some serious audience attrition, Everett strips down to her panties and bra to sing a plangent aria of loss. Then, in another quick turn, she clicks on her best throaty belt and, wielding a fake sledge hammer, sticks her face in an unsuspecting guy’s groin, singing this lyric: “Why you comin’ home, five in the morn? Somethin’s going on, can I smell yo dick?” The sleepy audience goes wild for it, and the show – unformed and seemingly under-rehearsed throughout – ends on an undisputable high note.

In his introduction to “Sexercise,” outgoing TBA guest Artistic Director Mark Russell called it “the throbbing, beating heart of this festival.” Clearly he was kidding us. Or maybe just himself.