Incest!
It was said in at least one episode that Cletus and Brandine are related in more ways than just husband and wife. (I can’t recall the exact quote at the moment)
ETA - ah Wikipedia to the rescue!
In “Alone Again, Natura-Diddily” at an auto racing event, Brandine remarks “Dang, Cletus! Why’d you have to park so close to my parents?” to which Cletus responds, “Now honey, they’s mah parents too!”
In the Season 16 episode, “There’s Something About Marrying”, Homer (ordained over the Internet as a minister) is preparing to marry Cletus and Brandine. Looking at a form, he asks “Wait a minute… are you two brother and sister?” Brandine coyly replies, “We’s all kindsa thangs.” To complicate the issue further, Brandine remarks to Cletus in another episode (“The Italian Bob”) “Yer tha best husband – and son – I’ve ever had.”
Seinfeld had a character named “Sal Bass”, who may* or may not have been Salman Rushdie in disguse (due to the fatwa).
*They were real, after all.
Pash
An episode of Seinfeld had George trying to get his parents’ attention by going on a date with his cousin.
While the topic of muslims on The Simpsons has been covered, there is one more that I can think of.
Krusty used to have a Sideshow Rahim who Krusty remembered as an “angry, angry young man.”
In addition, Krusty once wished his audience “a merry Christmas, happy Chanukah, kwazy Kwanza, a tip-top Tet, and a solemn, dignified Ramadan.”
South Africa?
Elaine’s white boyfriend was from South Africa.
Richard Gere and the gerbil? South Park? Gay divorce?
There was an episode of The Simpsons where Homer comments about something to Bart, who is watching South Park (or a parody thereof)
And while not actually gay divorce, there was the episode where Homer started marrying gay couples, and Patty almost married, but then backed out (because her lesbian lover was actually a dude.)
I don’t know if this is true or not, but from this site
EVERYONE IS TIRED OF THAT RICHARD GERE STORY was the blackboard gag in episode 5F01: “The Cartridge Family”.
The Holocaust, 60 years later and it’s still not any funnier.
“More dogs!”
Well, Jerry did get caught making out with his girlfriend while at the theater watching Schindler’s List
And don’t forget:
“You there, fill it up with petroleum distillate! And re vulcanize my tires, post haste!”
Not to mention the time he and George were abducted by Neo-Nazis. It’s not a direct reference to the Holocaust, but at least they were Nazis (or were they just white supremacists? I can’t remember exactly now that I think about it)
They were from the Ayran Union… so yeah, Nazis.
Oh, Plus there was a Soup Nazi!
In the Simpsons episode where Abe Simpson (Homer’s father) was going to marry Jacqueline Bouvier (Marge’s mother), Homer said (paraphased) “If my father marries your mother, that will make us brother and sister. And our children will be freaks with pink skin and five fingers.” He then looked at Bart, Lisa and Maggie, who morphed into normal looking children, and he shuddered.