Author's Note
This is just something I threw together after getting the idea at 1:30am on New Year's Day.
It's not perfect, but that's for you to decide.
One-Shot
You've only been in Equestria for a few months, but you like to think that you've adjusted quite well to the sudden change. Being yanked out of your comfortable life by causes unknown and dumped in a world of talking ponies came as a bit of a shock, but that's all in the past; you've moved on, and bettered yourself.
A new year will be dawning in a matter of hours, yet you are surprised to find very little in the way of preparations being done by the townsponies. Where you expect to see piles of fireworks, crates of food and kegs of booze, you instead see neat little piles of various items that will soon be sold in the market.
An explanation is required, so you decide to find Pinkie Pie – the one pony in town who could tell you what the plans for a New Year's Eve shindig would be – and interrogate her for answers.
It doesn't take long to find her; if she's not with her friends, she'll be at Sugarcube Corner, eating the merchandise. You march up to the counter and slam your hands on it, getting Pinkie's attention.
"Oh hey, Anon!" she chirps. "You seem a bit mad today, so why not tell your good pal Pinkie what's on your mind?"
"I want to know if you have a party planned for later tonight," you reply. "And, if you do, I want to help you out."
Pinkie cocks her head at you. "Party?" she asks. "A party for what?"
You waggle a finger at her. "Don't play silly with me, Pinkie," you say in a jovial, but still a little stern, manner. "It's New Year's Eve, so you've gotta have something up your proverbial sleeves!"
"New Year's Eve?" Pinkie looks perplexed. "What's that all about?"
"Seriously, Pinkie." you sigh. "Knock off the 'clueless' act. You can tell me what your plans are; I promise I won't tell a soul."
"I'm not acting, Anon." Pinkie shakes her head. "I genuinely have no idea what it is you are talking about."
You study her face for a moment, after which you realise that she is being serious. Your own face falls and you grab her by the shoulders, narrowly resisting the urge to start shaking.
"You don't celebrate the start of the New Year?!" you shout.
Pinkie tears herself away from you. "Why would we need to do that?" she asks. "It's not like we celebrate any new day; if we did, I'd be busy twenty-four-seven with party planning!"
"B-but, the New Year's Eve party is a time of great celebration!" you tell her. "It's a chance to reflect on the events of the past year, while at the same time looking forward to what the new one might bring!" You pause for a moment, a small grin appearing. "It's also an excuse for me to get blind drunk, wear a lampshade on my head, and do the Charleston on any table within leaping distance."
Pinkie giggles nervously. "Well, we don't do that in Equestria," she says. "If we want to reflect on past events, we just talk about them whenever we feel like doing so; we certainly don't need to devote a specific day of the year to it, like you humans seem to."
"We don't devote a day to it," you retort. "We're just as capable of reflecting whenever the hell we feel like it; it's just that New Year's Eve is the best time to do it, because it's like a fresh start."
Pinkie shrugs. "Well, be that as it may, Anon, I'm sorry to say that I won't be organising a party for an event that nopony celebrates." she offers you a sympathetic smile. "But, if it makes you feel any better, I can bring the girls round to yours for a small party."
You slump your shoulders. "I guess so," you mutter. "But before we have a party, there's something I need to organise first." You rub your hands together eagerly. "After all, I can't exactly have a New Year's Eve party without any fireworks..."
"Wait a minute, Anon." Pinkie holds out a forehoof, but you pay her no more attention as you turn around and leave the building. You've got a party to plan, and you're going to make damn sure it's one that everypony in Ponyville will remember for a long time.
***
Two Days Later...
Well, yours was certainly one hell of a party; everypony will be talking about it for the next few months, but it wasn't without its setbacks, such as running out of booze early, but chief amongst these being the fact you are now being held in Canterlot dungeons on various charges, most of which seem a bit over the top.
You're not accepting said charges, of course; it's not like you knew that Cloudsdale was actually flammable, nor could you exactly control where the fireworks would go after you lit them. And as for the ponies who got singed, well... surely it's their fault for being in the wrong place at the wrong time?
Celestia wasn't impressed, and neither was Luna; both of them were in Cloudsdale at the time and they both got a bottle rocket to the flank for their troubles. Laughing at the bandages wasn't exactly the brightest idea you've ever had, but you couldn't help it.
Consequently, you spent your New Year's Eve and New Year's Day in a cell — not that it's not the first time this has happened. Then again, you were only facing a charge of being drunk and disorderly the last time; according to your legal counsel, you are now facing charges of terrorism, arson, assault with a deadly weapon, illegal possession of explosive ordinance, breach of the peace, vandalism, holding an unauthorised public event, and – because you were 'callous' enough to hurt the Princesses – treason.
You stretch out on the bed in your cell and stare at the ceiling; a smile soon turns into a grin, and you chuckle heartily.
"Best. New Year's. Ever."