These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Only Fools and Horses
Big Lipped Alligator Moment: Rodney's nightmare at the beginning of the first chapter of the 1996 Christmas trilogy, "Heroes and Villians", in which a grown-up Damien not only runs Trotters Independent Traders, but also rules the western world in the year 2026, declaring war on other countries. While Del Boy, Lord of Peckham, and Raquel live a luxurious life in Trotter Towers, Rodney himself is reduced to being an old messenger, Cassandra is a maid after Damien took over her bank and fired her, and Uncle Albert's body has been preserved, repeating his trademark phrase on a constant loop. As Rodney berates Damien for ruining everything, Del wakes him up.
Fanon Discontinuity: Although the standard of humor is held up quite well, many fans ignore the 2001-03 Christmas trilogy because it completely ruined the perfect ending of the original finale; the 1996 Christmas trilogy, where the Trotters at last achieve their dream of becoming millionaires... apparently only for Del to lose it all on the Far East stock market. (Though they did gain a sizeable portion of it back through Uncle Albert's will in the final, final episode.)
Despite this, the very last episode "Sleepless in Peckham" is considered quite touching, especially when Rodney and Cassandra finally have their daughter, Joan Trotter Jr.
One particular detail that needs highlighting is that the end line of the first 'last episode' was, "This time next year, we could be billionaires," a very nice twist on Del's defining catchphrase. And was spoken as he, Rodney and Albert walked into a gleaming sunset. After 2003, the end line would always be, "D'you know Rodney? That's a bloody good idea." Which doesn't quite have that same ring to it.
Perhaps a real-world case of Be Careful What You Wish For. Its status as Britain's most popular sitcom meant that writer John Sullivan had been asked about a return almost constantly. And to give him some credit, he was trying to keep a sense of perspective. The wider context of the original sunset ending was Del enthusiastically trying to persuade the other two to invest in the market that was said to have crashed - and which had done so not long after the episode originally aired.
Interestingly, Sullivan originally wrote for the 1996 sunset ending to be done as a cartoon, indicating that the characters were no longer in the real world and would not be coming back, but this was rejected. (Though the sequence was eventually done with chromakey special effects.)
In the 1983 Christmas special "Thicker Than Water", Reg Trotter returns, and comes close to convincing his sons that he isn't really Del's father. Much later, the 1987 and 2003 Christmas specials "The Frog's Legacy" and "Sleepless in Peckham" would suggest that Rodney wasn't Reg's son (although "Thicker Than Water" already had a pretty strong implication of that itself - or at least that Del had reason to have always thought it was a possibility, yet he didn't know the truth until a drunk Albert told him).
In the 1992 Christmas special "Mother Nature's Son", the Trotters attempt to pass off tap water as "Peckham Spring Water" — it glows in the dark due to dangerous contaminants. Coca-Cola would proceed to do this when it launched Dasani in the UK. That and the discovery of carcinogens led the product being pulled. When Dasani was found to be just filtered mains water, it got nicknamed "Sidcup Spring" after this episode and the location of the Dasani bottling plant. Which just adds to the parallels with the episode, since Del managed to pollute the 'Peckham Spring' water with some chemical dumped in the reservoir (that caused the water to literally glow in the dark).
In her initial appearance, Raquel mentions that until that point her career highlight had been a small role in an episode of Doctor Who — which was intended to show how spectacularly unsuccessful she had been as an actress, since the show's ratings and reputation were a complete joke by that point, and it would be cancelled just under a year later. Exactly 25 years later the actress who played Raquel, Tessa-Peake Jones appeared in Matt Smith's final episode as the Doctor, with the show's reputation pretty much the opposite of what it was when Raquel first appeared.
Never Live It Down: In the latter episodes, Rodney and Cassandra were fond of bringing up the art contest and subsequent holiday in "The Unlucky Winner Is..." whenever they needed an example of Del's mistreatment of Rodney, to the point where Del even lampshades it in the 2014 Sport Relief episode.
At the very least, nearly everyone agrees that the 2001—2003 trilogy is markedly weaker than the rest of the series. Some consider the series to have been at its best when it was just two guys and their grandfather/great-uncle trying to pull off "get rich quick" schemes, and that its initial premise was derailed by the introduction of Cassandra and Raquel.
The series' original format based on "get rich quick" schemes alone was starting to grow stale around the time of the 1987 Christmas special "The Frog's Legacy", which was a good reason to bring Raquel and Cassandra in to freshen things up.
Values Dissonance: Del's homophobia, which was Played for Laughs in a way that reflected society's attitudes at the time the early seasons were filmed. Interestingly, the show noted the change in opinions - Rodney is much more accepting, and calls Del out when he suspects that he could have gotten Aids from an effeminate hairdresser.