Last Day to Live

A comedic storyline where the characters have been told that they have accidentally been poisoned, or have contracted a terminal illness, and only have one day left to live. The characters typically go around doing things they would never do otherwise: Rob a store, Insult some very tough-looking bikers, confess their feelings of true love to someone who doesn't reciprocate....and then they find out they aren't actually going to die after all. They are now screwed. See also The Last Dance, Your Days Are Numbered and Like You Were Dying.

Examples of Last Day to Live include:

Anime and Manga

Full Metal Panic!, where Sousuke orders a thermos full of a new form of liquid bioweapon. He brings it to school, go figure, and the entire campus is locked down. Hilarity Ensues. It turns out to only dissolve fabrics. ....almost all fabrics.
Van Zant and Smitty's initial reason for killing people during the Majin Buu Saga of Dragonball Z essentially amounted to this, as Zant wanted to kill as many people as he could due to the world ending with Majin Buu and wanting to go out with a bang. It's also viciously done in that not only did the end of the world end up not happening because Mr. Satan managed to teach Majin Buu right from wrong, but their nearly killing Mr. Satan as well as Bee the puppy when attempting to kill Majin Buu so they could kill more people ended up triggering the apocalypse due to Buu forcibly expelling his evil self, and then being absorbed by it.

Film

Max Keeble's Big Move is the kid-friendly version, with the catalyst being his family moving out of town rather than death.
Crank. Although he intends to survive somehow. ~~He doesn't.~~ He does.

Literature

The book How I Spent My Last Night On Earth is all about this- there's a rumor on the Internet that an asteroid will hit the Earth in a few hours, so the heroine finally finds the courage to confess her love to her crush. The rumor turns out to have been only a rumor in the end, but she and a lot of her friends are happy about it because they finally were able to do similar things.

Live Action TV

Testees did it when Peter and Ron were told they had accidentally been injected with a cyanide-like solution (really an experiment to see how they would react).
Used in Dead Like Me, Mason gets a purple post-it instead of the usual yellow and thinks this means he's going to reach his quota. After moping the entire day and selling all his possessions, the next day everyone gets a purple post-it. What? Rube was out of yellow. It's more of a Last Day to Be Undead, but...
- It's more likely that Mason had thought the purple post-it meant that Rube had found out about him killing Ray, and that's also why he was so convinced that that day was going to be his last.
In Star Trek Deep Space Nine, Quark is told he's contracted a deadly disease. In an effort at settling his debts and earning a place in the Ferengi profit-based afterlife, he sells his corpse. Of course, after he learns that he's going to live, he finds out that his arch-nemesis bought said corpse, and is determined to collect.
Red Dwarf, "The Last Day": Kryten reaches his expiry date. Being a thoroughly selfless mechanoid, he has to be coaxed into getting drunk instead of spending his last evening folding his shipmates' laundry.
Even Stevens: While not actually dealing with death, this trope still applies: In one episode, the Stevens were going to move to Washington D.C. after Mrs. Stevens won the Senate seat, so the family tried to live out their last day in their hometown to do things (Ren Stevens having her friends paired up with a lookalike, Louis Stevens finally taping his feelings for his female friend, and Steve Stevens... well... telling off his boss.). Of course, once it turns out that they wouldn't be moving to Washington D.C. after all (Turns out they mixed up the ballots, which means it was actually her opponent who won the election.), they immediately attempt to rectify the situation. It's also subverted in the sense that Steve Stevens ended up refusing to rejoin his job in the end despite attempt to get it back, as well as Louis Stevens receiving a video from his crush explaining her feelings for him as well by mistake (he originally intended to get back his own tape). Played straight with Donny, though, as his coach ended up in Washington D.C. because he never got the memo.
The final episode of Heroes had this trope forcibly being placed onto HRG (Claire also was trapped with him, but for obvious reasons, she was exempt from this trope). After Samuel Sullivan buried the prize trailer that HRG was held in and Claire Bennet got trapped trying to save HRG, he ended up giving up hope on living and telling her to escape without him when Claire was desperately trying to get them both out. He only managed to survive another day along with Claire due to Tracy Strauss getting them out with her water abilities at the last second.

Video Games

Subverted in Metal Gear Solid Peace Walker, when Coldman managed to activate Peace Walker's launch protocol and its ability to leak data to NORAD, because he knows full well he is going to die before the consequences of his actions could come to haunt him if it turned out they would launch, and he actually does end up dying, even going as far as to do so before divulging the abort code (and it is heavily implied that he intended to die before giving out the abort code so there is no way they could stop it.).
Inverted in Batman: Arkham City, Thanks to Joker's usage of TITAN in the end of the first game, he had at least six more months to live as a disease was ravaging his body, and attempts to find a way to get out of his predicament. He ends up dying at the end of the game.

Western Animation

The Simpsons did it when Homer was believed to have eaten a poisoned fish at a Japanese restaurant.
- Later in the series, Homer is following a self-help book. He reads "Live each day as if it were your last"; Smash Cut to him sitting on a curb, sobbing about how he doesn't want to die.
- When he thinks the world is going to end at sundown, Smithers kisses Mr. Burns. When it doesn't...

Smithers: Uh.. sir.. er, about that kiss. I hope you understand that it was merely a sign of my respect.
Mr. Burns: Yes, yes, of course.

Dexter's Laboratory had an episode where after eating a burrito Dexter gets stomach troubles and thinks he's going to explode in two hours. He had a last day "To-Do" list that consisted of setting his robots free, bouncing around a rabbit costume he hated to make his mom happy, building an indoor bowling lane for his dad, and giving DeeDee permission to run amok in his lab. At the end, he goes to tell his parents about the secret laboratory and instead farts so hard he blows the TV partially through the wall. Right after his dad told him to "Let 'er rip."
This was the plot of The Flintstones}} prime-time special "Fred's Final Fling".
There was also an episode of The Jetsons, when George believes he's gonna die, and signs up for profitable but dangerous job that involves testing a prototype worker's uniform that is allegedly indestructible. He finds out the truth at the most inconvenient time and panics. Luckily the experiment still succeeds, only to fail for completely unrelated reasons.
Inverted in an episode of SpongeBob SquarePants - the titular sponge is thought to have unknowingly eaten a deadly pie, which will end his life at sunset. Squidward, responsible for bringing a pie-shaped bomb to Spongebob, feels guilty enough to spend the rest of the day doing anything Spongebob wants. It's eventually revealed that Spongebob never ate the bomb-pie, but rather a different pie. He saved the bomb, which he promptly trips and thus throws into Squidward's face, producing a nuclear blast.
Hey Arnold!: Helga Pataki gets kissed by a monkey and believes that she has contracted monkeynucleosis. She believes she's going to die and even soon finds herself on her death bed, her health failing. She decides to tell everyone exactly what she really thinks of them and give them her stuff. Eventually, she brings Arnold into her room to tell him her true feelings, but before she can her friend barges in and reveals that monkeynucleosis doesn't really exist and that Helga won't die after all. And thus, Helga's secret lives on.
Family Guy did a variation that involved the entirety of Quahog being affected with this trope: On April Fool's Day, the newscasters mention that a black hole had suddenly appeared and that in a few hours the Earth was to be sucked into the black hole, only for it to be revealed at the last possible moment that it was actually a very horrible April Fool's prank, and Peter admitted that his children should never have been born during what he thought were his last few moments in life, and guess what happens for the remainder of the episode.
The second episode of American Dad had the family thinking they had be exposed to a virus that would kill them in a day, so they spend the time watching the first season of Twenty Four.
In a Recess episode, they find a fortune paper, and Gus gets his fortune read that states "Eat, Drink and be merry, for tomorrow is your final day.". He then decides that, as his "final day", he might as well engineer a reubin-style trap for school bully Gelmon to end his bullying once and for all. After his friends fortunes end up being doublesubverted as duds, it became apparent that Gus's trap will most likely backfire on him. It did, in a sense: When Gus was taunting Gelmon to lure him into the trap, Ms. Finster, being completely unaware of Gus's trap, attempts to break it up, with Gus trying to warn her not to get closer. Too late, as she ends up taking the trap instead (which is enclosing her in a cage with a banner in a similar manner to a zoo that read "Don't feed the Gelmon", which also got Gelmon fearful upon the realization of what Gus was trying to do, apparently traumatizing him from the close call enough to actually make him terrified of the people he formerly bullied, and Gus got detention until 6th grade for his backfired trap.
In Arthur, thanks to a very cruel prank by Arthur and Buster meant to get revenge on DW for eating a Green potato chip that they intended to do something with, DW became terrified enough to believe that she would actually die from eating a green potato chip, and decided to do what she can for her supposed lingering days, also telling Binky Barnes (who himself ate more than one), who then decided to take up dance lessons, whereas DW treats Arthur nicely and attempts to kiss him goodnight. She only learns the truth when, after witnessing Arthur about to eat a green potato chip, she snatched it away from him in order to save him.

Real Life

Real life example, for some inadequately explored reason people thought the world would end in 1998, there were even radio adverts preparing people for their last day on Earth. This was in England by the way, and after said last day? Life continued as normal and never mentioned again.
Many will probably be acting the same way in 2012.^[context?]
May 21, 2011 anyone?^[context?]