It isn’t the exact quote that gave birth to the old Wilma Askinas aphorism, but I’ve always remembered it as “A friend is someone who sees through you and still enjoys the show.” Truman Capote and Tennessee Williams were contemporaries so superficially similar that you can’t imagine that they were ever friends.

But they were. Apparently, they could see through each other yet still enjoyed “the show.”

Through ups and downs, jealousies and blasts of “bitchery,” Williams and Capote were connected for nearly 40 years, two titans of American letters who saw themselves as rivals but who pleasantly coexisted in the rarified air of art. They corresponded, complimented or (lightly) insulted each other in televised interviews, met up at parties or in restaurants and even took joint vacations with their respective partners during their vacationing days.

Drawling, florid Southern homosexuals who were “out” long before that was done, or safe to do, they make a fascinating, intensely quotable pair of wits in “Truman and Tennessee: An Intimate Conversation,” a documentary built on their relationship with each other, their art, their respective psyches, fame and the world they lived in.

To-the-manner-born filmmaker Lisa Immordino Vreeland, who has made documentaries about her mother, fashion editor Diana Vreeland, as well as arts patron Peggy Guggenheim and photographer and set designer Cecil Beaton, rounded up the many interviews Williams and Capote had with David Frost, Dick Cavett and others and juxtaposed them in near-conversation form. Here is how each answered questions about fame, reputation, writing, fear, “superstition,” love and happiness. Frost in particular hit each with the same sorts of questions which makes for a marvelous compare-and-contrast exercise.

We see generous snippets of screen adaptations of their work — movies such as “The Rose Tattoo” or “In Cold Blood,” “Breakfast at Tiffanies” and “The Glass Menagerie.”

And Vreeland cast actors Jim Parsons (as Capote) and Zachory Quinto (as the darker-voiced Williams) to read from their letters, memoirs, plays and books — sometimes droll, occasionally playful, cutting or confessional — to create a fascinating portrait of two giants who had a lot more in common than we ever could have guessed.

Williams was a dozen years older, and always presented a kind of weary, boozy and fey gentility. The much-imitated nasal whine of Capote could be grating or amusing. But the man never could keep a lid on his ambition, ego and vanity, even when trying to feign modesty.

“I invented myself,” the New Orleans native born Truman Streckfus Persons noted. “And then I invented a world to fit me.”

Capote was first moved to write after discovering the artistry in Melville’s “Moby Dick.” Thomas Lanier Williams III was “obsessed” with the playwright Anton Chekhov, which might be, he admits to one interviewer, because “the South (could be) so much like Czarist Russia.”

Capote (he took his stepfather’s surname) takes pains to deny his constant self-promotion, even as it related to his grand “society” statement, his lavish all-star/all-upper class 1966 “Black and White (Costume) Ball” in Manhattan’s Plaza Hotel. Please, Williams wrote, when relating the reasons why he turned down the invitation.

“People are never so unattractive as when they think you are worth impressing.”

Capote could be gloriously cruel to those he might be feuding with — their mutual friend, the also-ran novelist Gore Vidal, for instance. But the meanest on-camera remark he dropped about America’s most decorated playwright was “Tennessee’s not intelligent,” in trying to make a point that artistic achievement doesn’t always correlate with native or educated intelligence.

But the obvious point of comparison here is quotability, and Williams wins that contest, hands down. His anecdotes and his ability to see, analyze and succinctly sum up human foibles are what made “Truman and Tennessee” for me.

“Life was a wonderful basket of gifts that (Capote) loved digging through,” he said of his friend. “He took, and he shared.” But above all else, “Truman wanted to be famous and loved and envied.” That’s the tidiest description of the “famous for being famous” celebrity ever written.

Capote talks of wanting to “rescue from anonymity…the ‘girls’ (like Holly Golightly of “Breakfast at Tiffany’s”) who come to New York,” and of what researching and writing “In Cold Blood” cost him psychologically.

Williams breaks down “The Glass Menagerie” (which is about “the necessity to break tender bonds”) and “A Streetcar Named Desire,” and the rapid fall his career experienced after 1960.

And Parsons and Quinto sound just enough like the real writers to make this an almost seamless, often revealing and always entertaining look at the two writers, letting us see them as they were each other, two men of letters cut from very similar cloth.

MPA Rating: unrated, drug and sexual content

Cast: Tennessee Williams, Truman Capote, David Frost, Dick Cavett, with Jim Parsons and Zachory Quinto

Credits: Directed by Lisa Immordino Vreeland. A Kino Lorber release.

Running time: 1:25