Charles Maze and Andrew Oswald in Regrets Only at Diversionary.

You’d think Tibby has it all. Husband Jack’s a mover/shaker attorney. They have a posh-plus, Upper East Side apartment (which, in Matt Scott’s fine set for Diversionary, looks down on Manhattan). Daughter Spencer’s an up and coming lawyer. And Tibby’s best friend/confidant’s Hank Hadley. Yep, THE Hank Hadley, world-class fashion designer. And maybe best of all, Jack doesn’t seem to mind that Tibby spends so much time with a man — in part because Hank is gay. That his companion of 31 years died recently makes Hank even more available.

Jack prefers to stay at home. Hank and Tibby paint the town so much she has to write “regrets only” replies to the soirees and fundraisers she can’t attend.

Tibby’s so fashion conscious, she’s over-the-top-and-through-the-woods, as when she asks, “It’s a bit chilly out. Do I need a bracelet?”

Jack’s got a sense of humor too. When the Oval Office phones him to fine-tune the Federal Marriage Amendment, he says it was “the President of the United States — or, at least some of them.”

It’s 2006. President George W. Bush wants to enact an amendment defining marriage as “solely of the union of a man and a woman.” Self-satisfied Jack, who could give a hoot about marriage equality, jumps at the chance, as does Spencer, though she wants to know both sides.

Apolitical Tibby just jumps. While Hank gets an idea taken from Douglas Turner Ward’s one-act “reverse mistrel show,” Day of Absence, in which all the African-Americans disappear from a Southern town, leaving white folks to forge for themselves. Hank’s thought: what if, in protest to the amendment against gay and lesbian marriage...

Regrets Only questions how to define love in person and under the law. But Rudnick presents his theme like a Midwestern tourist testing the shore-break at P.B. — toe in, toe back: marriage for all; marriage sucks; love is love and not fade away. It’s a scatter-gunned, passive-aggressive, take your pick approach. If he makes a major assertion, as if afraid he’s offended someone, he immediately undercuts it with a joke.

But ah — the jokes! At least a third generates depth-charge roars, which gives Regrets Only one of the best comedic batting averages in years.

But how to play them? The characters are, at the same time, looney tunes and hurting human beings. So tone everything down?

For Diversionary, director Jessica John offers a sparkling alternative: make BOLD choices. First and foremost, the McCulloughs, their maid, and Hank are performers. Always on stage, relentlessly theatrical, they act as if in a “Lives of the Rich and Famous” reality series. But when the pain hits, the masks fall.

No weak links in the cast: Kerry McCue (a new face locally) somehow makes Tibby puddle-deep and touching. Andrew Oswald does his best work to date as Hank, and has a real knack with asides. Charles Maze as straight-laced Jack, Teri Brown as the intrusive maid, Myra, ever-versatile Rachael VanWormer as Spencer, and a whacko cameo by Dagmar Krause Fields (in one of Peter Herman’s classic fright wigs) as Marietta. None go gently to that spotlight, and credit the director for precise, and hilarious, ensemble work.

Special mention: do a show about a world class designer? Better bring the goods. Alina Bokovikova’s costumes elegantly fill the bill, as do a jewelry showcase window’s worth of diamonds.