For those of you who like a bit more of a challenge, here's another criteria:

The summary can't just be the 'it gives me a (probably correct) bad feeling', it's things that absolutely cannot be canon. For example:

Hermione is raped and tortured by Ron and finds solace with Draco. Not an AU.

I know, this wasn't a challenge to find badfic based on summaries, but I couldn't resist posting this from the Pit for Skyrim.

"One of the Divines toys with the feelings of mortals and immortals alike by throwing an innocent and beautiful woman from an other dimension in to Skyrim."

Thing I found a while ago but did not seek out has:

"Warning: r63 Alduin, Possible lemons, suggestive terms/content, and swearing will be present. The Dragonborn has began to question his purpose for living and Alduin takes the opportunity to fufill a strong desire. But, Did she actually satisfy more than just her own desires in the end."

what if Jim had a little sister? and what if she came with him to treasure planet? read to find out! :D i promes u wont be disapounted :)

https://www.fanfiction.net/s/10554707/1/Plants-vs-Zombies-Story-The-Adventure

"One day, someone dared Sunflower to drink one gallon of mixture wine, liquor, beer, and Mickey Finn in under 1 minute. Sunflower did it. This causes many crazy stuff to happen! Zomboss duplicates Zombies, a Camera Zombie spies on plants, PLANTS TURN INTO ZOMBIES, and Peashooter and Sunflower have A BABY! Read to find out what happens next!"

I simply thought it would just be a case of bad biology; it turned out to be a sickening combination of that, bad psychology, horrible pacing, and misuse of author notes. (And by that, I mean questions that show up at the end of each chapter in the most hammy writing style you can think of.) Also the fact that the author really, really loves order of magnitude and big numbers.

I've only done one fic so far where the summary sounded like a badfic but the fic itself was OK, and that was the one for "Of Swimmers and a Sue."

Seducing the Survivor:

https://www.fanfiction.net/s/11027444/1/Seducing-The-Survivour

Kelsier thought he'd planned for everything... but he'd never planned for THIS.

I say no more.

The one I thought of off the top of my head, though, is one I'm planning on sporking in a few missions:

"Castiel was a broken angel when Lucifer finally won on Earth. So when God gives him the chance to go back and stop it from happening, he was quick to agree. There was one catch...he would have to abandon his gender and become female to avoid a paradox. Now Castielle is on a mission from god to save the Winchesters and hopefully make things right between her and Dean. Destiel!"

Oh, and a very strange, short badfic in Spanish:

"Bella es una bruja, su nombre real es Lily, decide regresar al mundo magico a hogwarts, ¿que se escontrara alla? mal summary, soy nueva no sean malos"

(As far as I could tell, the translation is "Bella is a witch, her real name is Lily, she decides to return to the magic world of hogwarts, what will she find there? Bad summary, I'm new, not bad".) The entire fic was seven sentences of sheer wat.

"*Chapter 5* Hermione is half vampire, but only one person knows this. And what does she hold over him to make him do her bidding? ::sings:: It's gettin' hot! Hot! HOT!!"
"A chance accident strips Harry of his humanity and leaves him a creature of pure hatred. A creature who understands what has been done to him in the past and seeks ultimate revenge. Though at the same time Harry wishes to build himself an empire, built from the ruins of a society he will destroy. Powerful Dark Harry, Dumbledore and Weasley Bashing"
Generally speaking, if a fic's summary has "Powerful Harry", "Dark Harry", "Grey Harry", "X Bashing" and so on and so forth, then it's gonna be an OOC, possibly Suvian mess nine times out of ten.

A friend of mine recently mentioned a book to me during a discussion about the disgusting requests I've received over the years for fanfic. The most egregious example I brought up was regarding a certain nazi doctor, which led her to ask me if I'd heard of a book about "...blond and blue-eyed Jewess Hadassah Benjamin". And yes, that's from the first line of the summary. You just know it's going to be a great, compelling, realistic novel when the Jewish protagonist is "pressed into service by SS-Kommandant Colonel Aric von Schmidt at the transit camp of Theresienstadt" and "battling a growing attraction for this man she knows she should despise as an enemy."

From the Persona series:

"Kari Yuki, Yu Narukami's [the Persona 4 Protagonist's] adopted sister, moves to Inaba just weeks after Yu's arrival. What role will she play when it comes to solving the mystery? A loose re-telling of the story from Persona 4 (not Golden) with some hints of P3/P3P, told from Kari's point of view.
Rated T for now, but will change if required."

I count four major red flags for a Mary Sue in as many sentences.

I can also recall one case where the fic (also from Persona) had a generic 'I can't write summaries' but I could tell it was going to be very squicky from the M rating and the fact that the only characters were Mianko/Hamuko/Kotone (they're all names for the Persona 3 female protagonist) and Koromaru (the team's pet Shiba Inu). After an attack of curiosity, I was able to confirm that it was indeed sexually explicit yiff, and I very much regret clicking on it.