The fan fictions listed here are notorious to the point where they are often cited as the worst fan fictions of all time.
Rini's Horrible Death (2004)
This Half-Life fan fiction by squirrelking earned both infamy and then fame when a parody of it was made on YouTube. Despite its ridicule from the video, this story, along with its sequels, Half-Life: Full-Life Consequences 2: What Has Tobe Done, Half-Life: Hero Beggining, and Half-Life: Full-Life Consequences: Free Man, have gained cult followings, and are often used as memes.
My Immortal (200?)
This is a fan fiction loosely based on the Harry Potter franchise, often regarded as "the worst fan fiction ever written". It is heavily criticized for its OOC canon characters, its explicit spelling and grammar errors, its Mary Sue protagonist, and its crudely-written sexual content. Some people are debating over whether or not its author, Tara Gilesbie, was making a parody trollfic out of it. Before its removal from FanFiction.Net, it had over ten thousand reviews, most of which were flames. It is also well-known for being parodied by several other authors on FanFiction.Net, who use the exact same notorieties found in the original. On August 2, 2010, the story was revived by TheJadedDolphin.
A SpongeBob SquarePants fan fiction written by ikillfaguts, a user who is banned from FanFiction.Net. It was notorious for being racist and homophobic, as well as having content being too explicit for its proper rating. The most notorious criticism was that the story itself lasted only three sentences long.
The Death of Nick (2010)
A Total Drama fan fiction written by Nickspaz17, and was the last fan fiction written by him before his inactivity. Like most (if not all) of his stories, it received negative reviews, although this was one of his most panned stories. It is notorious for its OOC characters, its ridiculous plot elements, and its disturbing and explicit sexual content. The most notorious criticsm of all was the fact he was under the appropriate age of not only writing the story in its proper rating, but also too young to join the site (in which you have to be thirteen years or older to join).
A My Little Pony: Friendship is Magic fan fiction written by Sgt. Sprinkles. Its most notorious criticism was the explicit use of violence and gore when Rainbow Dash was killed by Pinkie Pie. Despite its awful reputation, it had become an Internet meme.
A Harry Potter fan fiction written by proudhousewife. It is overall a Christian version of the book series. It has mostly received overwhelmingly negative reviews, criticizing its OOC characters, degradation of the canon, and preachy propaganda. Some reviewers believe this story to be worse than My Immortal, arguably making this the "worst fan fiction ever written".