Their ubiquity was certified in October when the two, at the Arden Theatre's 25th anniversary celebration, sang songs from the 16 shows - apiece - in which they have performed under Arden artistic director Terrence J. Nolen. Sometimes alone (Coon in Sunday in the Park With George, Dibble in Candide), often together ( Assassins, Tulipomania, A Year With Frog and Toad), the number of Arden productions they've graced was a highlight of Nolen's onstage patter. "I can build my season around them," he said.
So could the venerable Walnut Street Theatre, where Dibble has performed in 10 shows and Coon in a whopping 29, including his current dream role as Harold Hill in The Music Man.
"The first Walnut show I ever saw was Music Man in 1984 [while] preparing for my first audition, my Lower Cape May Regional High production of that same show," says Coon, 41, who used "Sadder but Wiser Girl" for his tryout rather than "Seventy-Six Trombones" - other contenders used the more recognizable song, but he wanted to stand out.
It's a quality that has kept him at the forefront of directors' minds across the city and beyond. In May he'll play an egotistical Italian opera singer in Lend Me a Tenor at Act II Playhouse in Ambler.
"If I'm to name something that gets me cast so often, it's that I think I'm easy to work with, am a fast worker - usually off-book by the time we start rehearsals - and do my best to be a positive influence on the energy in a rehearsal room."
In other words, he plays well with others.
"Jeff is your ultratraditional handsome lead with a very rich baritone filled with powerful tenor notes who audiences love," says the Walnut's Bernard Havard, who is celebrating 30 years as the theater's president and producing artistic director. "Ben is a great singer too," Havard adds, "quirkier and edgier, but with a big voice. Audiences respond to him as well."
That would be Ben Dibble, 34, the other half of Must Die's dynamic duo. Currently preparing Henry V for a February opening with Lantern Theater Company and Arden's A Little Night Music for May, Dibble believes stage professionals respond to his precision and specificity.
"I'm often thanked for being in the right place at the right time. Seems simple, but it's actually a feat I've watched some actors struggle with. And my sense of play - I try to fill every process with joy," he says.
"My wife, a casting director, would say it's my voice, my attack on material, my bravery, and my inability to be embarrassed by anything I might do in public. She says I'm smart. She sees a lot of actors, so I guess she's right."
Beyond what each actor sees in himself, it's what artistic directors like Havard and Nolen see in them. "They just keep earning it," says Nolen. "They're committed to the work, have amazing voices, and are invaluable whether in an ensemble, the lead, or as support."
Nolen was the first director to cast Coon and Dibble together, in 2000's The Jungle Book, and he has been doing it ever since. "They just fit."
Because he has worked with both for so long, there are dialogues about what they hope to do in the future. Echoing what he said at the Arden celebration about building a season around them, Nolen notes that "you don't do Hamlet with open auditions - you have to know your lead before going forward."
"There are great musical theater roles as there are the classics of drama and comedy. Jeff and Ben set the pace. We have that relationship where I can say 'I can't do this play without you.' "
Havard takes it a step further, saying that beyond aesthetics there's a commercial reason that he casts these guys: "Absolutely, Jeff in particular has box-office appeal; Dibble has it too for us, though he's more of a chameleon and therefore less defined."
Still, is all that love from directors and audiences sufficient reason to want its objects subjected to the most final of final curtains?
"I think a part of every actor needing work - so, every actor - wishes the competition would die," says Tony Braithwaite, artistic director at Act II Playhouse and an actor who has worked with both men. "There's never enough work to go around, and many of us are - spoiler alert - neurotic about it."
Then there's Amy Dugan Brown, wife of Dibble, friend of Coon, and director of the show-as-death-threat in question.
"Professional envy is ugly, so J eff Coon and Ben Dibble Must Die went for broke, exposing how ugly and desperate show business - really, any business - can make a person," says Brown, who made sure the comedy served a deeper purpose than to simply point fingers and laugh.
"Besides, they were hugely flattered: How many people get their names in the title of a show?"