This is an index of tropes that are often indicative of plain bad writing.
When done unintentionally, these tropes are usually bad signs. When done intentionally, they're often signs of parody, comedy, or just the writer being ironic or stylized. Hopefully.
Please note that Tropes Are Tools, and many highly acclaimed works have used these tropes successfully.
Jerk Sue: Having a character be a complete Jerkass who gets away with it just because the author designates them as such and says you should support them does not make for a strong character, and is more likely going to turn out be a case of Creator's Pet, and often The Scrappy. Also, it tends to look like a half-assed effort when the author just throws in some secondary throw-away detail in an attempt to make you feel sorry for the character and expect you to not get upset when they behave like a jerk for no other reason than they feel like it at the time.
Out of Character: Moments when the character does something that he wouldn't normally do without any justification.
Positive Discrimination: Don't make the female or minority characters better than the others simply because they are minorities, and don't make the male characters incompetent simply because they are males.
Special Snowflake Syndrome: Make sure your character actually fits into the universe you've put him/her into. If your character doesn't fit (for example, elf mages fighting crime in the Big Applesauce), make sure there's a solid reason why they're there.
Villain Sue: A flawless, invincible villain who never loses at anything makes for a boring story just as much as an ordinary Mary Sue.
Wangst: Make your characters react realistically to setbacks or tragic events. Too much angst makes them unrealistic and annoying.
Wimpification: Stripping the action, common sense, and characterization from a male character to add Wangst and gender stereotypes applied to females is a good way to piss off many of the audience, including but not limited to feminists and actual gay or bisexual men.
Gratuitous Rape: Rape is an incredibly grave subject matter. Don't shoehorn in a rape scene just for shock value.
Idiot Plot: Unless it's part of their character, the plot should not be forced to move forward solely by people making stupid decisions.
It Gets Better: Just as the viewer shouldn't demand the work to end already as with Ending Fatigue, they shouldn't be forced to sit through hours of exposition or padding to get to the actual plot.
Just Eat Gilligan: If there's an obvious solution to the problem(s) that drives the story, you would think the characters would go for it rather than ignoring it.
Kudzu Plot: It's fine to have a dozen different story threads at once, but you have to be able to tie them together. If they go off into infinity without ever being tied, who's going to care about any of them? The pieces of your Jigsaw Puzzle Plot have to fit.
Author Filibuster: The reader/viewer/player/etc is (theoretically) interested in the plot. Stopping it so that you can talk about something that's important to you will only make them less interested in what you're writing.
Gratuitous English: Randomly popping in meaningless English words that you don't know the meaning of is a bad idea. If you want to write in English, know the meaning of your English and make sure it's grammatically correct.
Gratuitous Japanese: It's generally not a good idea to use random bits of Japanese unless you're a fluent speaker, lest you come across as pandering to Occidental Otaku. Either write in idiomatic Japanese and learn how to properly pronounce it if you need to, or just write in your native language.
Examples Are Not Recent: When writing an example, avoid using the word "recent." What's considered recent now won't be in a couple of years. It just makes more trouble for other tropers to edit out the word "recent" once it isn't recent anymore. Act as if every work that was ever published came out several years ago.
Square Peg Round Trope: Make sure that the example that you want to add fully fits the trope. If it's "not really an example", then it's not really an example, and it shouldn't be added.
This Troper: Writing about oneself in a Main wiki article. The goal is to make Main articles sound like a single person is editing the article, not multiple people. Besides, personal comments just clog up the articles.
Thread Mode: Don't clog up a trope entry just because you don't understand why it's there.
Type Labels Are Not Examples: Any relevant context needed to explain the example should be given in the example itself. Don't simply label it "type X" and force the reader to open a separate page just so they can understand what it means.
Weblinks Are Not Examples: If one has a trope example, one should write it down, in adequate detail, where it is relevant, not rely on a URL link to some other page to explain what it is.
Word Cruft: When writing an example, just stick to writing the example and try to avoid saying useless things that don't need to be said.
Painful Rhyme: Don't force rhymes. If something doesn't rhyme, you can make a non-rhyming song that can be just as good as a rhyming one, or try to find rhyming words that both describe what you want and rhyme.
Something Something Leonard Bernstein: Depending on your genre, this might actually be workable. But in anything requiring clear vocals, this is automatically bad, and even in more permissive genres overly relying on it is often a bad idea.
Vocal Range Exceeded: Don't write things your singer can't sing, and if you're the singer as well as the writer, be realistic about your range and capabilities.note A common mistake here is writing for the highest ranges such as pure soprano and alto. Especially among male singers, the capability to reach these ranges is vanishingly rare (male singers will usually fall somewhere between tenor and baritone on average), and even most female singers fall short of being capable of pure soprano or alto voice, and a singer who is incapable of such and tries anyway will likely sound falsetto and possibly damage their vocal cords. If in doubt, write for the lower ranges and modify higher.
Canon Defilement: People who are reading your Fan Fic probably enjoy the show for what it is. Not for what you would like it to be. Seeing beloved characters mangled into whatever form you desire is probably going to cut down on your audience, unless you're Neil Gaimannote And even he shows a great deal of respect for Canon while mangling it.
Dan Browned: If you haven't done the research, don't claim you have.
Demonization: Some of your potential audience may actually see where this position is coming from, if not actually agree. You'll turn them off by your exaggerated portrayal. It also makes it seem like the position you hold isn't nearly as solid as you think, since it can only stand up to strawmen.
Glurge: If you're trying to write a heartwarming story, make sure people don't find questionable things underneath your message before you do.
IKEA Erotica: Sex should only be as boring as it is to the participants.
I Suck at Summaries: If you can't be bothered to summarise your fic properly, then why should people be bothered to read it?
Narm (when caused by the writing): Make your dramatic/climactic scenes convincing, not cheesy. Don't go over-the-top. Make it realistic. Think about how a person in Real Life would behave in the situation.
Nightmare Retardant (when caused by the writing): If something is supposed to be scary, either don't show it or actually make it scary.
Strangled by the Red String: People going directly from being strangers to being genuinely in love is not very realistic or satisfying to watch. If you're going to make two characters fall in love with each other, try to take it slow.