Around the time of the Killers' 2006 second album, Sam's Town, Flowers grew a thick push broom worthy of that record's grandiloquent Americana.
Drummer Ronnie Vannucci one-upped him with a fearsome Fu Manchu, and bassist Mark Stoermer let his blond scruff run wild.
That album's unapologetic Springsteen-philia proved something of a critical brick, however, and Flowers' pronouncement that Sam's Town was "one of the best albums in the past 20 years" made the record ripe for dissenting opinions.
Those whiskers are gone now, and Flowers' preferred accessory for his Kimmel performance was a natty schoolboy jacket with feather epaulets.
Guitarist Dave Keuning wore a barely there synthetic tiger-print shirt, and the band's stage set-up was littered with glowing faux palm trees befitting its hometown of Las Vegas.
The Killers' third studio album, Day & Age, released last month, is their furthest-reaching yet: a melange of Roxy Music saxophone pomp, roller-rink disco and jittery synths supporting Flowers' newly surrealist lyrics.
Rock music is down to maybe a half-dozen bands who consistently reinvent themselves and still go platinum each time.
But after their grand ambitions for Sam's Town met a fairly resounding shrug from tastemakers - and moved about half of Hot Fuss' 3 million copies in the US - the question remains: Will the Killers' second attempt at an aesthetic makeover keep them in that ever-rarer clique?
"I let [those criticisms] affect me a lot," Flowers said.
"But one thing we gained from it was that when we came back to the towns where those reviews were, we'd just play louder and we became a really great live band. It took that confidence to do what we did with this album."
In some ways, Day & Age feels like a direct riposte to the earnest and old-fashioned American arena rock ideals behind Sam's Town.
The new single Human, a pillowy and remix-ready sliver of synth-pop, already has yielded one of 2008's most head-scratching and grammatically suspect choruses, now familiar to anyone who has spent time with rock radio recently: "Are we human / or are we dancer?"
Other lyrics seem to offer eulogies for the band's turn at whisky-and-highways mythology, like when Flowers asks to "Give my regards to soul and romance, they always did the best they could," or in Spaceman, in which Flowers ironically reassures himself that "The song-maker says it ain't so bad".
On Day & Age's first track, Losing Touch, Flowers more directly taunts the band's skeptics: "You go run and tell your friends I'm losing touch / Fill their heads with rumours of impending doom / It must be true."
But despite Day & Age's critical ruminations, the band's famed self-assurance seems to have survived the reception of Sam's Town intact.
"I love the challenge of playing to naysayers," drummer Vannucci said.
"I love that I can drive it home and make believers out of people."
The band usually doesn't have to try hard to do so: Upon striding into the Roosevelt lobby, Vannucci was instantly encircled by a small pack of starry-eyed autograph seekers.
Between songs at the Kimmel performance later that day, Flowers said to the crowd, "We only want to please you," reaffirming the idea that Day & Age's pointedly eclectic genre-hopping still aims straight at the audience's pop pleasure centres.
The laser-sharp funk bass lines of Joy Ride and margarita-ready bossa nova of I Can't Stay shouldn't have any business being on the same record, but the Killers have spent enough time on the pop charts to wrangle a worthy single from any stray arrangement idea.
"There's a big misconception that you can't be artistic or sophisticated and be big," Flowers said.
"We should be praised for being on alternative radio and pop radio and doing the things that we do. It's not like anything else."
Flowers (27) also has the future of a young family to look out for.
His wife, Tana, gave birth to a son last year, and the frequently eyelinered singer of a band who has written at length about cocaine blues (Uncle Jonny) and gender-swapping hookups (Somebody Told Me) is said to enjoy an unusually idyllic home life in Vegas.
Flowers' onstage presence as a fashion-flaunting rake is mercurial, however.
Along with his stable young family, he's quite possibly America's hippest Mormon rock singer.
Flowers makes a point of keeping his faith private and separate from his band's limelight.
Flowers' ideas about pushing rock music forward in a market of ever-dwindling album sales are some of the few systems that still seem to be working.
For all the make-or-break anxiety about Day & Age, the band made a point to carve out time for its third Christmas-themed single for (RED)WIRE, a new subscription-based music service benefiting HIV efforts in Africa.
Fashions, genres and lyrics about depressed neon felines come and go, but the annual holiday novelty hit is one thing that the Killers will never, ever waver on.
"As long as we're going, we'll have a new Christmas song every December," Flowers said.
Vannucci agreed: "You know that things are dark if we don't have a Christmas single."
