Actor Allusion: In the JFK parody in "The Boyfriend," Newman replicates his position standing in front of Kramer, just as Wayne Knight did in the movie standing in for John Connally in the courtroom demonstration of the "magic bullet" theory.
A picture of a dinosaur appears in Newman's apartment, referencing Knight's role in Jurassic Park.
In the episode "The Maid", Kramer is picked up by a stranger who is looking for a maid and asks Kramer if he knows how to use a mop wringer. Kramer's answer is yes.
Banned Episode: One of the last episodes of the series, "The Puerto Rican Day", was initially pulled after its original broadcast, mainly because NBC felt the episode was too offensive with its depictions of Puerto Ricans, as well as a scene involving Kramer (accidentally) burning a Puerto Rico flag, causing an angry mob of Puerto Ricans trashing the streets, and vandalizing Jerry's car (to which, Kramer remarks, "It's like this every day in Puerto Rico."). As of 2010, certain local markets across the country had placed the episode back into their packages; but as of 2012, the episode is now back permanently in the syndication package (Kramer's line, "It's like this every day in Puerto Rico" is absent, though it could be a case of being Edited for Syndication).
The Danza: Jerry Seinfeld's character is named... "Jerry Seinfeld."
George's mother Estelle is named after her actress. But they couldn't name his father the same way because they already had a Jerry.
But, George's dad was originally played by John Randolph.
In "The Kiss Hello", Wendie Malick as Wendie the delicate genius.
Descended Creator: As the show went on, Larry David had more and more Creator Cameos usually seen only from behind or voicing unseen characters like George Steinbrenner, a part David continued to voice for some time after he had already left the series as a writer.
Edited for Syndication: Most episodes feature little dialog cuts here and there to save time for more commercials. The episode which suffers the worst in this regard is "The Yada Yada", as it originally ran 26 minutes in its NBC premiere.
Since 2010, most markets air the episodes in a cropped format (similar to a x1.2 zoom on most DVD players), and as such, all on-screen titles (opening credits, closing credits, subtitles, etc) have been changed accordingly. Some episodes also have either repositioned the show logo in the opening, or left alone, resulting in half of the 'S' in Seinfeld being cut off.
Hey, It's That Guy!: Too many examples to list. For example, George and Jerry combined dated about 120 different women; all, but a small handful have shown up in other well known films and shows.
Hey, It's That Voice!: J. Peterman's actor can unmistakably be heard as the voiceover in current Coors Light commercials.
I Am Not Spock: It's happened to every cast member except Jerry Seinfeld. Particularly Wayne Knight. On one instance, after a bad day, he snapped at someone who greeted him with "Hello, Newman...". On the other hand, Jason Alexander once appeared on Real Time with Bill Maher, and one of his fellow panelists agreed with him by saying "You know, George is right..." Cue a big "OOOOOOOH" from the audience. Alexander, however, laughed it off with a good-sported remark that "Hey, I'm still getting the royalty checks."
Alexander also got into a bit of quote call-backs during some hands at the 2010 World Series of Poker, and once mentioned he was grateful for George Constanza, because he'd otherwise be known as the guy who tried to rape Julia Roberts.
During the Laugh Factory incident, various media outlets kept referring to Michael Richards as Kramer, to the point that the real Kramer, Kenny Kramer, issued a statement saying that he personally was not a racist.
Speaking of Curb, even earlier than that, in season 2, a plotline revolved around Larry trying to get a show off the ground about an actor who can not escape their previous popular sitcom role, first with Jason Alexander and then with Julia Louis-Dreyfus.
Missing Episode: "The Puerto Rican Day" has a scene where Kramer (accidentally) burns a Puerto Rican flag. Many viewers were highly offended, and NBC decided to leave the episode out of syndication for several years. Although it does occasionally air on local stations today, many stations still skip it (including TBS) and those that don't often cut out the flag-burning scene. You can see it uncut on DVD, though.
For a time, "The Invitations" was removed from syndication because Susan dropping dead from licking toxic envelopes reminded people of the anthrax mail scares. It returned to rotation in summer 2002.
Old Shame: Regis Philbin loves the series, so he was disappointed that when he guest starred, he was given a line that he didn't think was funny (three variants of "This guy's bonkos!"). The producers insisted it would be hilarious, but his lines didn't get very many laughs with the studio audience. To this day, Regis dreads watching that episode for that reason.
The Other Darrin: Phil Bruns originally played Morty Seinfeld, but after his initial appearance, he was played by Barney Martin.
Larry David originally played Newman in "The Revenge" (he provided his off-screen voice), but his first on-screen appearance was by Wayne Knight. In syndication, Knight dubbed over David's voice in "The Revenge" to provide some continuity. However, both versions of the episode are available on the DVD set.
John Randolph originally played Frank Costanza in "The Handicap Spot". Later, Jerry Stiller replaced him in "The Puffy Shirt". For syndication, John Randolph's scenes in "The Handicap Spot" were re-shot with Jerry Stiller in his place, to provide continuity. However, as with the previous example, both versions are available on DVD. One weird effect of this is that George says his father is bald in an earlier episode, which fit Randolph but not Stiller.
Lloyd Braun was initially played by Peter Keleghan, and later played by Matt McCoy in "The Gum" and "The Serenity Now".
Playing Against Type: Daniel von Bargen, who almost always played stern, humorless authority figures, here is the shiftless and irresponsible Mr. Kruger.
Throw It In: The ending of the episode "The Parking Garage". Originally, the four of them were supposed to get in the car and drive off. But the car they had had an undercharged battery and wouldn't start. After all the frustration of shooting the episode, they realized that the car being dead was just so much more perfect than anything they could have come up with.
Jerry's line in "The Junior Mint," "Let's watch them go slice this fat bastard up." His quickly taking a sip of coffee afterwards was to keep from laughing.
What Could Have Been: Larry Miller was originally cast as George, but it was decided that, just to make George a little bit more pathetic, he needed to be short. Miller eventually appeared as a doorman that could give The Janitor a run for his money.
The project began as just a 90 minute special about a day in Jerry's life, and how it inspires his stand-up material that night. Jerry and Larry David couldn't quite stretch the script to fill the 90 minutes, so they reduced it down to a half hour as a series pilot. As Jerry would later say, "We couldn't make 90 minutes, so we made 90 hours."
Elaine's father was intended to be a recurring character, but then they hired the notoriously ill-tempered and intimidating Laurence Tierney to play him, and after filming the episode, no one wanted to work with him again. Among other things, Jason Alexander and Jerry were genuinely intimidated, and Tierney was seen stealing knives from the apartment set.
The waitress in the pilot was meant to be a recurring character, but the producers thought she was too abrasive and the show needed a female lead, so Elaine was written in.
An episode called "The Bet" was scripted but never produced. When the script, whose plot revolved around Elaine buying a gun, reached the table read stage, it came off as unfunny and unnecessarily dark. Pretty much everyone present realized on the spot that the concept wouldn't work, so the entire script was shelved.
"The Bet" lives on as an Internet urban legend in the form of a "creepypasta" story alleging the episode was filmed and all but one copy destroyed. Naturally, the episode supposedly contains disturbing and supernatural phenomena happening to the actors and crew.
Write What You Know: Larry David based the George character off of himself, and many of the plotlines allegedly were based on real life experiences he had, and how he reacted to them.
(paraphrasing) Jason Alexander: This is ridiculous. This could never happen to someone, and even if it did, no one would react that way.
Larry David: What are you talking about? It happened to me, and that's exactly how I reacted!
Kramer was based on David's neighbor Kenny Kramer.
This was even parodied in the series: In "The Muffin Tops", Kramer starts his own bus tour, proclaiming himself to be the real J. Peterman (to differentiate himself from the anecdotes he supplied to J. Peterman's autobiography). This mirrors real life, as Kenny Kramer has run Kramer's Reality Tour and Kramer's Reality Road Show, the gimmick being that he's the real life Kramer.
In addition, Bob Balaban's recurring role of Russell Dalrymple, the fictitious president of NBC who works with Jerry and George on a television pilot and later becomes Elaine's love interest, was modeled on then NBC Entertainment president Warren Littlefield, who had allowed David and Seinfeld to produce the Seinfeld pilot. Balaban later went on to play Littlefield outright in the 1996 film The Late Shift, a dramatization of the struggles that occurred at NBC when Littlefield selected Jay Leno to replace Johnny Carson on The Tonight Show, instead of David Letterman.
The famous Soup Nazi was based on a real soup kitchen owner in New York. He did not take it well, and banned the entire cast and crew of the show from ever coming to his kitchen.
Written By Cast Member: Jerry Seinfeld co-wrote at least one (and usually more than one, especially in the early years) episode in all but the last two seasons.