I went to a theatrical comedy last night and witnessed one of the least funny things I’ve seen in a while. The unfunny thing that took place was not part of the play on stage. It happened in the audience.

I’d gone to see Threshold Repertory Theatre’s production of Dinner With Friends, the Donald Margulies play widely praised for its unflinching depiction of marital shipwrecks and their repercussions. Two couples, long-time friends, wrestle with the new normal when a divorce threatens to break up the group. That divorce is a shocker but one of Dinner’s themes is that no one outside a relationship and looking in has a clue what’s going on beneath that surface. It’s hard enough for the people directly involved to keep track.

While people got their seats sorted out, the pre-show music playlist set the tone. Among the songs, Graham Nash sang “Our House,” his ballad to then-girlfriend Joni Mitchell and the simple pleasures of domesticity. “Life used to be so hard, Now everything is easy, ‘cos of you.”

The theater began to fill.

A forty-something couple sat down next to me and he launched into the kind of small talk — carefully neutral in tone and topic — that’s demanded when companionable silence is not an option, when silence itself might be taken as a reproach, even an indictment. His wife murmured responses distractedly. “You look nice tonight,” he said and she acknowledged the bland compliment, but kept her hands folded in her lap and her gaze on the crowd still milling about.

The play began. In the third scene things got fiercely unfunny onstage. Divorcing couple Beth (Pamela Galle) and Tom (Jay Danner), loosed broadsides on one another with the ballistic accuracy that only formerly loving couples can achieve. It was heated. Then over-heated. The man down the row from me leaned into his wife’s ear and whispered something. Then he rose from his seat.

Maybe it was the four-letter-word language onstage. Maybe it was the intensity. The man got up and our entire row fidgeted their legs aside to let him and his wife pass. Through all this commotion (and while the fleeing couple crossed not three feet away from them) the actors didn’t miss a beat.

It’s a pity that couple didn’t stay for the entire show.

Later in the play, Gabe (Laurens Wilson) has a line that drew a good deal of laughter.

“All marriages go through a baseline wretchedness,” he says.

Later still, Gabe and his wife, Karen (Erin Wilson), sift through the debris of their divorced friends’ late, unlamented marriage and weigh up the value of their own. It’s worth waiting for this concluding scene. It says a lot about the ties that actually do bind.

Dinner With Friends offers a caveat to theatergoers that reads, “Recommended for Mature Audiences Only.” Perhaps they should also warn that couples going through a “rough patch” might want to look elsewhere for date-night entertainment.

And I’m thinking that another Crosby, Stills & Nash song could be mixed into the pre-show playlist — Stephen Stills’ “Helplessly Hoping.” Because that song recalls that at some point in each of our relationships we all feel a little like harlequins “awaiting a word.”