In case you missed the 1968 Broadway run of Tennessee Williams’ “The Seven Descents of Myrtle” — and, let’s face it, you did — the film version, “The Last of the Mobile Hotshots,” is a virtual advertisement as to why the thing tanked: because it’s terrible.

Any excitement you may feel walking into the movie blind is certainly understandable judging from its pedigree — James Coburn and Lynn Redgrave starring in an X-rated adaptation of a Tennessee Williams play, scripted by Gore Vidal (“Myra Breckinridge”) and directed by Sidney Lumet (“12 Angry Men,” “Long Day’s Journey Into Night”). But that enthusiasm is sure to melt quicker than an ice cream cone on a searing summer’s day in the bayou, where the movie is set.

If you didn’t know it was based on Williams, the film’s arduous structure, egregious flashbacks and penchant for allowing its cast to launch into long, tedious monologues instead of, you know, engaging in recognizable human conversation would certainly make you cringe. Fact is, I did know it’s based on Williams and it still bugged the hell out of me.

Jeb (Coburn) and Myrtle (Redgrave) meet on the set of a game show, where the host offers them $3,500 and a slew of appliances if they marry on-air. The duo take the bait and shuffle off to Jeb’s ramshackle plantation, which he insists he wants to renovate. Trouble is, Jeb’s half-brother Chicken (Robert Hooks) also has designs on the place, and the movie is more or less 100 minutes of the three of them bickering and squabbling with each other while a pending storm threatens to flush the whole lot of them into the Gulf.

There are other details at work, such as useless stabs at character development (Jeb is impotent and dying of cancer, Myrtle is fixing to start a new life, etc.), but these drips are such hateful, repugnant (and, in Redgrave’s case, incredibly annoying) people and the stakes are so low that you literally wait in agony for that storm to bust that levy and wash all of this unpleasantness off the screen once and for all.

★