At the end of the lonelygirl15 episode "Backyard Bikini Patrol", Sarah remarks, "Us girls had a kickass day today. And, you know what? Tomorrow is gonna be even better!" The following day, in "Tick Tick Boom", villain Salinas sends her a video of her boyfriend Bound and Gagged with a bomb strapped to his chest.
Also in "Partner Swap", the day before prom night, Emma comments, "I have this feeling that we're going to have the most memorable night of our lives." In the next episode, "Prom: It's To Die For", Gina is killed.
Occurs all the time in the Protectors of the Plot Continuum. Whenever an agent says anything along the lines of "At last, a break from badfic." or "Now I can catch some sleep." he/she/other/it get sent to another mission. Lampshaded by references to the "Laws of Narrative Comedy". If a mission is described as appearing "not too bad", it will rapidly get worse.
DesuDesBrigade: After learning of the aforementioned Project D being done at a NASA base, Hitch said, "I am so outta here the moment they mention space vampires!" Much later in the review, near the end, when the vampire tells Kuki about their battle with evil aliens across the universe...
Hitch: Done. I am not doing space vampires! No! Done. Done! Dammit!!
In part 2 of Metroid Confusion, the two protagonists are blasted into space by a nuclear explosion. As they drift pointlessly through space on a piece of rock, the following exchange occurs:
"Look on the bright side. It could be worse." "How could it possibly be worse?" (rant detailing the situation they're in) "It could be raining." "You idiot! It cannot rain in space!"
It seems that when anyone tries to review the godawful Batman & Robin film, it is almost a requirement to suggest that it won't be as bad as it's made out to be ( like RiffTrax and The Nostalgia Critic, with the latter providing a quote). In the case of the Critic, not less than 15 seconds after saying so, he tries (and fails) to pop a cyanide pill.
Throughout the Critic's review he's been doing this a lot. He said that a current scene would be even cheesier if a certain special effect is used or quote is said. And then that happens anyway.
Zero Punctuation illustrates this concept with DC character Dr. Fate being offered cake.
There's also the "[PROTOTYPE] vs inFamous", where Yahtzee declared both games to be equal and jokingly said that if the game studios want him to pick a winner, they'll have to send him their best images of the rival game's main character wearing women's lingerie. Much to his surprise and horror, they complied.
Yahtzee: Thanks to Radical Entertainment and Sucker Punch Productions for being such good sports. You sick, sick fucks.
The Spoony One sang a parody of Rob Van Dam's entrance music during one of the first episodes of Wrestle! Wrestle!, with cheesy lyrics about himself ("Duh-da-duh-da-duh! It's time for the Spoony One's! Duh-da-duh-da-duh! Wrest-ling show!"), then remarked "Watch people ask me to make that the theme song." You get three guesses as to what WW's theme song is, and the first two don't count.
Also in his Pokémon Colosseum Let's Play, he confuses Dakim's Camerupt and says that now that it's confused, let's hope it does something stupid. Camerupt then used Earthquake, taking out Dakim's Shadow Entei.
Metal Gear Awesome: After being incinerated by lasers and blown up by mines, Snake mentions: "Oh gee whiz, I sure hope a tank doesn't totally come out of nowhere and OWN me!" Cue the tank totally coming out of nowhere and owning him.
In Tabletop, Wil Wheaton mentions that one of the reasons he likes Zombie Dice is because nobody ever gets out to a huge lead. Cue Ryan Higa rolling ten brains on the first turn (out of 13 required for victory). The tempting of fate was exacerbated by the other players egging him on to keep rolling, believing that his luck was going to run out on him.
Web serial novel OH GOD THE RAPTURE IS BURNING starts the entire epic story with a sentence that sums up everything you need to know about Tempting Fate: "Rapture's nothing but bullshit." The title of the story comes from almost the very next sentence, so you can imagine how that turned out.
Often deliberately invoked in Cracked. Whenever the list asks "What could be worse (scarier, bigger), than that?", the next item invariably will.
The Let's Play ofKnights of the Old Republic II: The player, during the fight against Darth Nihilus, ends an update with a vote on whether he should try to fight him normally or have Visas sacrifice herself to weaken him through their Force bond. The very last words in this update are "And don't say both or I'll murder a puppy. Multiple puppies." The very next update, which goes with the first option but also shows how the second would play out, is titled "The Puppy Holocaust", with video of the second option "brought to you by the flayed corpses of a thousand little adorable puppies".
This is apparently starting to become Ray's schtick in Rooster Teeth's Let's Play series with the phrase "Is there fall damage?". This stems from an LP of "Trouble in Terror Town" where he leaps off a roof and asks, mid jump, that phrase. There is and he dies, leading the terrorists to win that round.
This is probably true for any game they play, be it Minecraft, Grand Theft Auto IV, Worms, Halo - if things are going their way and someone says something to tempt fate, then they'll get it in the behind.
A Running Gag on TV Trash is for host Rowdy C. to set up a situation by saying that there's no way they could do [insert something truly despicable here], then cut instantly to just that. He's even lampshaded his tendency to tempt fate many times.