So after my last description was called into question, I've decided to try to put together a clearer idea of what a crack ship is.

A Crack Ship is a ship whose premise makes no logical sense.

Example:
(Quote curtesy of cleverpun)

Is Pinkity () a crack ship? No, because they could logically end up together: they're friends, they enjoy each others company, and they spend a lot of time together.

Is TrixiMac () a crack pairing? Possibly. They have very little contact with each other and have highly conflicting personalities. But they did encounter each other a few times in passing in canon, so it would depend on the setting of the story.

Is DitzyBelle () a crack pairing? I'd say yes: they never interact, have a huge age difference, and have absolutely nothing in common. The default initial reaction is "say what?" and while good writing or fan interpretations may change the former attributes they don't do much for the latter.

As we can see, DitzyBelle is cleary defined as a crack ship under this definition, but Pinkity isn't, because there is a logical reason for it's existance. TrixiMac is more subjective, however, and can't be easily placed in one catagory or the other.

In this case, i would be tempted to listen to my gut and call it a crack ship. However, others might object to this.
And that's okay. Each story should be analysed on a case by case basis. If the premise, the idea the story is built around, makes no sense, it's a crack ship. If it does make sense, it's a regular, if uncommon, ship.

Feel free to tell me I'm wrong post your thoughts below.

Edit—Just like to point out, that OC's (pony or otherwise) do not ever count as crack ships. I don't care how crazy/different/opposite to their partner they are, they are not crack ships.

I see...to me, Pinkity is a crack ship. There are very few mane6/mane6 crack ships, and to me, this is one of them. TrixMac and DitzyBelle are also crack ships. (How many times have you seen either of these ships together.)

It's really just a matter of the pairing's plausibility, IMO. I'm gathering that the original definition you used, which is pretty much what I've been going by as far as this particular group was concerned, was a little too liberal? Plausibility is an entirely subjective thing, unfortunately. Everyone has their own ideas.

As far as I'm concerned, none of the Mane6xMane6 pairings could ever be considered crack ships. There's too much foundation for a relationship within canon because of all the interaction they all share in like every single episode. There's also no other circumstances that might be well, squicky or weird, such as difference in species and whatnot that make you think 'what the fuck' (like there would be if you wrote a fic of Pinkie getting plowed by Gummy).

I'd argue that the other two examples are crack ships, because those ponies have little to no interaction with eachother in-show, or any interaction between the two is not of such a nature so as to make the pairing reasonable. Those pairings are implausible because those ponies have nothing to do with eachother, so the premise of the pairing is irrelevant.

910673
You seem to be confusing crack ship (a ship which doesn't make sense) with an uncommon ship (a ship with few, if any, fanworks dedicated to it).
Pinkie Pie and Rarity are not only friends, but also are very similar. Both want to make their friends happy, one through laughter and one through generosity. This mutual intrest binds the two together, and makes for a plausable ship.

910782
Agreed. Mane6XMane6 is just to plausable to be a crack ship.

And basing crack ships of the lack of interaction (romantic or otherwise) between ponies in the show is a perfectly valid method.

Also, I think GummyXPinkie exists somewhere. I'm kinda scared to find out.

910896
No, I don't think there would be

If a crack ship is a ship whose premise makes no logical sense, how logical the readers think the premise is mostly gets based on how well the author bothers to / is able to pull it off. Dash x Scootaloo could usually be considered a crack ship (Scootaloo likes Dash, so they bang!), but on the other hand Best Young Flyer is a thing that happened.

Take Gilda x Prince Blueblood. That's a weird pairing that, to my knowledge, no one has ever written before. Given that they have no on screen interaction and have no obvious reason to be attracted to eachother, it'd naturally be a crack ship, and if you wrote it with the emphasis on how strange the idea is (If you take this route I'd suggest "Prince Blueblood's Fabulous Feather Fixation" for a title), then you'd be right. Put a [Comedy] or a [Random] tag on that, and you'll be golden. And also probably slightly confused afterwards.

But if you wrote a story where Blueblood started thinking that everyone who mocked him after the gala was actually out to get him politically, and subsequently hires Gilda on as a bodyguard because she's quite intimidating, and then they villain-bond over Gilda teaching Blueblood malicious pranking strategies to get back at his political rivals, and you start moving the two into bodyguard crush territory as they come to realize they don't really have any other actual friends and they start opening up to each other...

It's not as straightforwards to write as something more fanon conventional like AppleDash--you gotta get down in the trenches and explain to people how this really does work--but its still quite plausible if you have the writing chops to make it plausible, and if you can make it plausible people won't think of it as crack shipping despite it being a story about Prince Blueblood wanting to nuzzle Gilda's downy-soft feathers.

Hm.
what about Things such as LyraMac or TwiTavia?

Alot of people treat LyraBon and VinylTavia like they're canon, even though we have little/no evidence to support it.

Does it fall under Uncommon, sense the evidence is so circumstantial and they have had possibilities of interacting, or Crack ship?

I third the idea that Main6xMain6 can't qualify as crack ships.

911073
One of my points in my previous post was that you can't use good writing to justify a ship as non-crack. Your initial reaction to the story is still going to be surprise, even if the content later changes your mind.

912326
Fanon characters are weird cases, because the fan interpretations are such big parts of the character. I don't think it's unreasonable to treat fanon as important, considering we are talking about fanfiction in the first place.

Shipping Vinyl or Octavia with anypony besides each other is going to provoke surprise, even if that wasnt intentional. Since all background ponies technically have no canon personality anyway, I think the uncommon pairings you mentioned count as crack ships.

Fun fact; the Crack Pairing page on TVTropes lists OctiScratch as the first example. Entry must be really old by now.

910896

And basing crack ships of the lack of interaction (romantic or otherwise) between ponies in the show is a perfectly valid method.

Keep in mind that when the two characters in question get like 1 second of shared screentime together (in for example the next season), this might change.

912326

LyraBon and VinylTavia

These are dubious cases, since this is 'fanon' for a lot of people by now. Besides, I'm pretty sure these have separate groups already, so apparantly they're big/popular/not-crack-anymore by now to achieve such status. So my 2 cents on this is while they should be crack, they've been so overdone by now, that it's not really crack anymore.

I think it was a while back that I saw 'The Great Shipping Collab', which had ships like Daring Do x Zecora, or Cadance x Big Mac, for example. Now unless these suddenly get hugely popular for whatever reason, even if they do it's been crack for three seasons now (unlike LyraBon which was pretty much fanon after S1). And it are things that should make anyone go 'wat' anyway.

Yeah, quality of writing is definitely not a factor in whether something is a crack ship or not. A good writer can make anything make sense, and we should, uh, celebrate that and not exclude it?

I'd qualify the defining trait as... 『Dis-Intuitivity』. If you can look at a pairing and, based on your past experience, understand why they'd be shipped together without having to read the story, it's not a crack ship. This, conveniently, rules out ships that should be crack, but are too common to be considered as such i.e. Tavi/Vinyl.

An understandable basis for a relationship can be pretty varied, though. Obviously, the kind of friendship between any of the mane six is enough to build off of. Likewise, a notable antagonistic connection can work: Trixie/Twi, or Celestia/Discord. A basis doesn't have to limited to the source material, though, as long as audience on average would be familiar with it, it counts. So we can rule out like, Lyra/Bon and Soarin'/Braeburn.

I suppose of all that only rules out what a Crack Ship isn't. I think that's the only way to define it, though, it's a ship with an absence of reasonable expectation, so in order to figure out what counts, you have to draw a line around what ships do make sense.