
Got to talking recently with a friend about capturing the essence of various musical genres in a single line. Thought I’d take a shot. In alphabetical order:
The Blues – “If it wasn’t for bad luck, I wouldn’t have no luck at all.” – Albert King (recorded 1967)

This is from Albert’s “Born Under a Bad Sign,” a song title that may well capture the genre as well as the chosen line within.
Runner-Up: “Bright lights, big city… have gone to my baby’s head.” – Jimmy Reed (recorded 1961)

From his song “Bright Lights, Big City.” (FWIW, I almost went with “Big Boss Man… Can’t you hear me when I call?”) My favorite blues musician. Some critics say that Jimmy simply did the same song over and over again. I say, “We should be so lucky.”
Country – A tie:
“Will the circle be unbroken?” – The Carter Family (recorded 1935)

Timeless, not to mention timely (!), question at the root of both country music and our culture at large.
“I’m so lonesome, I could cry.” – Hank Williams

Covered by 100s, has a sadder song ever been recorded? (Check out versions by Al Green and B.J. Thomas) Gets me every time I hear it.
Folk – “This land was made for you and me.” – Woody Guthrie (recorded 1940)

Fun Fact: With a melody borrowed from the Carter Family, the lyrics were written in critical response to Irving Berlin’s “God Bless America” as sung by Kate Smith.
Runner-Up: “The answer, my friend, is blowin’ in the wind.” – from Bob Dylan’s 1960 song “Blowin’ in the Wind”

Hip Hop/Rap – “Don’t push me cause I’m close to the… edge; I’m try-ing not to lose my head.
(It’s like a jungle sometimes… It makes me wonder how I keep from goin’ under.)” – Grandmaster Flash & The Furious Five

From “The Message” (recorded 1982). Stuck in traffic on Boston’s Tobin Bridge, I was behind the wheel of Hyde’s school bus, full of Hyde basketball players en route to a big game, when a voice a few rows back took command of the team boom box and yelled up to me, “Yo, Mr. Gauld, we got something you need to hear!” And then the bus filled with this song. Had never heard anything like it in my life.
Runner-Up: “We be to rap what key be to lock, But I’m cool like dat; I’m cool like dat… I’m cool.” – Digable Planets

https://www.flickr.com/people/39075416@N03
From “Rebirth of Slick (Cool Like Dat)” off their 1992 debut album Reachin’ (A New Refutation of Time and Space). A former student also turned me on to this group. (Ah, boarding school life is so rich!) I still listen to this album.
Jazz – “It don’t mean a thing if it ain’t got that swing.” – Duke Ellington (1899-1974)

Kinda hard to come up with a definitive quote for a decidely instrumental genre, but it indeed seems fitting to single out The Duke and his 1931 composition with his celebrated-world-wide orchestra.
Runner-Up: “Strange fruit hanging from the poplar trees.” – Billie Holiday (recorded 1939)

From “Strange Fruit” by Billie Holiday. The angriest song ever recorded.
Miscellaneous: You might check out Ben Sidran’s 1987 song “Good Travel Agent” where he submits three essential ingredients for any serious jazz musician: 1) a bad romance; 2) a good travel agent (“… because nothing can get you out of town faster than a bad romance”); and, 3)… seafood.
Protest – “The Lord can make you tumble. The Lord can make you turn. The Lord can make you overflow, but… The Lord can’t make you burn.” – Randy Newman

His ode to Ohio’s Cuyahoga River catching fire in 1969. I was so obsessed with Randy Newman during college daze that a few of my buddies started called me “Randy.” Perhaps he would take some solace in the fact that the Cuyahoga is much cleaner today.
Runner-Up: “There’s a hole in Daddy’s arm where all the money goes.” – John Prine (1971)

From “Sam Stone,” Prine’s classic portrayal of the issues faced by too many Vietnam vets after returning home from “the conflict overseas.” Originally titled “Great Society Conflict Veteran’s Blues,” it presented a marked contrast to the way returning WW1 and WW2 soldiers were received by the general public.
Rock & Roll – “As I was motor vatin’ over the hill, I saw Maybellene in a Couple de Ville…” – Chuck Berry

Hard to pick just one. Heck, the runner-ups were a hard choice. But when it comes to rock & roll, I have two non-negotiables: 1) Gotta have both… rock and roll (i.e., not just rock), 2) “In Chuck We Trust.”
To me, this line is like the first part of the roller coaster when the chain pulls the car slowly to the top where it sits for maybe 2 seconds — the eery stillness fueling off-the-charts anticipation — before the freefall and ensuing emotional mayhem. It is such a metaphorically fitting beginning for a song that was, in turn, the beginning of Chuck’s career. (“Maybellene” was his first charted hit, peaking at #5 in 1955.) It also featured the Chuck Berry tradition of inventing new words: “motor vatin.” (Other examples: “Botheration” from “Too Much Monkey Business” and “Hurry-home drops” from “Memphis, Tennesee,” describing the tears of a young girl.)
I cannot say it any better than the late great John Lennon: “If rock & roll had another name, they’d have to call it Chuck Berry.”
Runner Up #1: “It’s gotta be rock & roll music, if you want to dance with me.” – Chuck Berry
Runner Up #2: “I know, it’s only rock & roll, but I like it.” – Rolling Stones
Rhythm & Blues – “R-E-S-P-E-C-T… find out what it means to me.”

Again, hard to pick just one. And for me, it’s equally hard not to go with Aretha.
Runner-Up #1: “Have you heard the news? There’s good rockin’ tonight!” (1993 version) – Solomon Burke (1940-2010).
Runner-Up #2: “I got a woman, way over town, That’s good to me, oh yeah.” – Ray Charles

From “I Gotta Woman” (1958).
And it’s all good to me… Oh, Yeah!
Onward, Malcolm