The "Phones-4-You" ad campaign goes from being a mildly successful attempt at Memetic Mutation to being pretty hilarious once you've played Metal Gear Solid 4, where the weapons merchant has a hand-gesture catchphrase for the slogan 'EYE HAVE YOU'.
It is generally quite hard to deliberately engineer a Hilarious in Hindsight moment, as it's all too easy to be offensive or to simply pander to an obvious in-joke. For a master class in doing it right, step forward the late, great British comedian Bob Monkhouse. Four years after his death in 2003, with thanks to modern digital wizardry, he appeared on television in an advert suggesting the wisdom of being tested for prostate cancer, cracking jokes about it being an even bigger killer of men 'than (his) wife's cooking!' so that the viewer doesn't end up 'as (he) did' - spoken while appearing standing beside his own actual tomb-stone.
At the time it aired, a McDonald's commercial featuring *NSYNC and Britney Spears playing "spin the bottle" had a rather light-hearted punchline, whereby the bottle stops on Justin Timberlake, not Britney. A few years later, Lance Bass came out as gay, and it gives the ad a whole new meaning.
A drug PSA showed Pee-Wee Herman (Paul Reubens) talking about how dangerous crack was. Reubens would later go on to play a drug dealer in the movie Blow. Then again, he had already been in some Cheech and Chong movies, which are about drugs.
A 1996 This is SportsCenter ad featured Karl Ravech and Keith Olbermann interviewing former Senator Bill Bradley for a job. The last line of the commercial has them questioning whether he'd spoken in front of an audience. Bradley says he gave the keynote address at the Democratic National Convention. Olbermann replies, "We meant a large audience." One that a decade later he himself would try to tap.
T-Mobile made a series of anti-AT&T commercials, very closely modeled after Apple's infamous "I'm a Mac and I'm a PC" ads. Mere months later, T-Mobile was almost absorbed into AT&T.
Alltel Wireless also ran a series of ads spoofing their competition, with takeoffs of AT&T, Verizon, T-Mobile, and Sprint "employees" featured (and the Verizon character often the butt of the jokes) — until merger talks between Alltel and Verizon heated up. The Verizon character was quietly dropped late in the campaign — shortly before Alltel itself was dropped into Verizon.
Lebron James appeared in a State Farm commercial where he dreamed of playing for the Cleveland Browns. The team they were playing? The MIAMI Dolphins.
Also, one infamous Sega CD commercial has become this. "You still don't have a Sega CD? What are you waiting for, Nintendo to make one?!" Nintendo was actually the last console maker to get into using optical media (though despite a common misconception, Gamecube and Wii discs aren't CDs—they're more like DVDs).
In a way, Nintendo had the last laugh on this one. They actually did attempt to contract with Sony to develop a CD-ROM add-on for the SNES. The deal went sour, resulting in Sony developing the device into a stand-alone console which went on to become a significant factor in Sega's exit from the console market altogether.
What's also damning about that ad is the majority of the characters listed in it are no longer shown on the network.
Another Cartoon Network promo. The time, early 2000s. Cartoon Cartoons Kings and Queens of the Network, Scrappy Doo and his fellow Hanna-Barbera cartoons forced out to be shown less in favor of Cartoon Cartoons. The time, early 2010s, Warner Brothers has released about half of their Hanna Barbera offerings to DVD, and very few of the Cartoon Cartoon offerings. One seems to sell so much better than the other, Take ThatCartoon Network
Back when Enron was viewed as a thriving corporation, they released a series of commercials with the theme "Ask Why?" Years later when Enron suddenly went Bankrupt shocking the country, the United States government asked them why? They got their answer when they discovered years of corporate fraud.
In some old Windows 95 commercials (such as this one here), Microsoft used a 2 by 2 grid of squares that were colored the same way as the Windows flag in order to demonstrate certain features, though it wasn't their official logo. 17 years later, Windows 8 shows up with a more tablet-oriented UI. Guess what their logo turns into?◊
The Brazilian arm of Fiat made an ad related to the 2013 Confederations Cup, entitled "Come to the Street", described as "the biggest bleacher of Brazil". Given that at the same time huge protests emerged in the country, the revolted people embraced it as an anthem. "Come to the Street" became their motto (along with "The Giant Awoke", taken from a Johnnie Walker ad) and was stamped and sung everywhere.
Sarah Michelle Gellar did an ad for Burger King complaining that rivals do not have as much meat, she was about six at the time. Today she has less meat than some girls at the same age she did the ad.
Also, the rivals in Gellar's Burger King commercials included McDonalds. Thirty years later, Gellar would play an advertising executive on The Crazy Ones. Guess who their first client was.
In a Dutch ad for distance education service LOI, well-known lawyer Bram Mozkowicz is involved in a - very minor - traffic collision, and is stunned by the other party's legal knowledge. In 2014, an automobile police chase in Amsterdam came to an abrupt halt when the perpetrator's car crashed into Mozkowicz's Aston Martin, with Mozkowicz inside. (Thankfully, nobody was hurt.)
A Singaporean ad about problem gambling which airs on 2014 FIFA World Cup shows a group of children discussing who would win. It then cuts to a depressing shot of a sad young boy hoping for Germany to win, as his dad bet all of his son's savings on them. Well, depressing until hours later, when Germany beat Brazil 7-1, and eventually winning the whole thing.
During his time with the NBA's Charlotte Hornets, star power forward Larry Johnson did a commercial as part of the Converse "Grandmama" series where Johnson (as Grandmama) was stuck in three-point land and needed to get to the low post. Partly because of a 1993 knee injury, Johnson would later develop into a decent outside shooter for someone in his position; with his most famous individual play coming at the end of game 3 of the 1999 Eastern Conference Finals between the New York Knicks (which Johnson had joined in 1996) and Indiana Pacers when Johnson hit a three-pointer that became known as a "four-point play" due to Johnson being fouled and sinking the free throw for the winning points in the 92-91 victory en route to the last-seeded Knicks winning the series in 6 games and going to the NBA Finals.
An Italian toy company named Giochi Preziosi has a collectibles division named Preziosi Collection. Each of it's commercials end with a white ghost mascot swinging his arms and pointing them as he sings the company's jingle. A few years after the first ad with said tag aired, Yo Kai Watch would have an opening credits sequence where a white ghost character who looks similar to the company's mascot does a similar dance along with other characters.