NAFTA
401(j) (the one that makes money)
Arrow’s Impossibility Theorem
Neumann-Morgenstern Utility Function
Deutsche Forschungsgesellschaft fÜr Druck- und Reproduktionstechnik (FOGRA)
Tukey’s Honestly Significant Difference (HSD) Test
Spj¥tvoll and Stoline T’ Test
Landy’s Opponent Process Theory
Least Preferred Coworker (LPC) Measures
Monetarism
Mercantilism
Gower’s Coefficient of Similarity
**Antidisestablishmentarianism **
Ehlos-Danler Syndrome Number Seven
Cheating at Canasta
The Battle of Issus
The Harlem Globetrotters Meet Cthulhu
CONCACAF
Joukowski airfoils
Cyanohydrin formation
The Way Orange Juice Tastes After Brushing Your Teeth
The Tuskegee Syphilis Study
Unconscionable
SEATO
The Great Leap Forward
How great Tang is
Dark energy
The Crimean War
How much you like them female’s butts
I’m pretty sure there’s more than one rap song about this.
turnips
awnings
Subdermal Hematomas
Sudden Infant Death Syndrome
Defenestration
President Chester A. Arthur
Necrotizing Fasciitis
The Origin of Consciousnes in the Breakdown of the Bicameral Brain
The Protestant Ethic and the Spirit of Capitalism
The Elementary Forms of the Religious Life
I do believe you are on to something here, Boyo Jim. Although my greatest expertise lies in areas other than the genre of Rap music, I could easily imagine situations where this music style could at least occasionally embrace the theme of female posterior appreciation. Good work. 
Vandermark v Ford Motor Co.
Monopolistic Advantage Theory
Selective Factor Disadvantage
Consonance-Dissonance Theory
the Great Vowel Shift
Oligarchy
Global warming and its effects on brine shrimp
Ask for ideas seldom referenced in Top 40 songs is kind of like asking for words that don’t rhyme with monkey.
I went to my congressman and he said , quote, “I’d like to help you son, but you’re too young to vote”
Summertime Blues
“you’re old enough for war, but not for votin’”
Eve of Destruction
“Why are little ones born only to suffer
for the want of immunity or a bowl of rice?”
Rush, Roll the Bones
At this point it should be noted that repeats are bound to happen. That being said:
Fibonacci Numbers
Euclid
Mating Strategies of the Romans
The Parallel Postulate
Van De Graf Machines
Panpipes
The Legend of Zelda
The Mayflower Compact, and similarly, The Fundamental Orders of Connecticut
The Plight of Elves in Scandinavian Countries
Capitalization
Scented Candles
Platelets
The “Punched-In” Bottoms of Wine Bottles (Called the Kick, or Punt)
Hemophilia (?)
The Anus of a Horse
When Dogs Circle a Few Times, then Lay Down
The Reformation
The Great Migration
How cool I am! How attractive I am! How amazingly awesome I am! But you just wait, someone will make me a tribute song
necrophilia
Aquaman
President Franklin Pierce
tungsten
the top quark
ibexes
gry
Tuvalu
lichen
calzones
women’s golf
phlogiston theory
Zeppo Marx
And similarly, denderphilia
And me, killing this thread 
I believe there is or was a band named Vaginal Cream Davis…
- semi-automatic PDF generation
- Linux
- Open-source politics
- CNN censorship
- People being kidnapped by four-dimensional women, like in that Rudy Rucker book
- differences in cellphone frequencies and transmission standards throughout the world
- vermicomposting
- magnetic screwdrivers
- calendar reform
- popcans
- the metric system
- dropping a lamp
Eminem (A.K.A. Marshall Mathers, A.K.A. Slim Shady) included this in his latest single about his mother, “Cleanin out my closet.”
However, the literal sense of cleaning out your closet is not something commonly referenced to in Top 40 songs.
Neither is:
The switch from the Julian to Gregorian calendars
The Great Schism
St. Polycarp’s own Epistle to the Philippians
The Whitewater scandal
The Iran-Contra affair
CIA intervention in Latin America
The Wave of Depolarisation in a neuron undergoing a stimulus
Sin, Cosin, and Tangent
Paralellograms!
Schwann Cells
A Practical Critique of Shakespeare’s Comedies
The Year of 40 Roman Emperors
Irrational numbers
Famous Rabbies
Pythagorean Theorum
Intercourse outside the species
The Golgi Apparatus
Hypochondria
St. Justin Martyr’s “Dialogue with the Jew Tryphon”