My personal hated tropes:
Romance
- the main character ALWAYS chooses either the childhood best friend or the random stranger they just met, and it's immediately visible whom the author ships
- if there are multiple people interested in the MC, somehow you never see the emotional fallout of the one that doesn't end up with the MC
- the "manipulative jerk" that is thrown in just to create tension, whether by trying to steal the MC or trying to make the love interest leave the MC
- the "evil mother" that decides the MC isn't good enough for their child (why is it ALWAYS the mother? My ex-mother-in-law was the cool one, it was my ex-FIL who was an asshole)
- why do stories with multiple love interests never seem to consider polyamory except to glorify it as a "harem"?
Fantasy:
- there's always a specific magical creature that the writer focuses on repeatedly as almost a mascot of their story, like Final Fantasy's obsession with chocobos, moogles, and cactuars; if it's a well-developed world with tons of magical creatures, there should be a variety actually represented in your story (if I ever succumb to this trope, my mascot will be airhogs... flying groundhogs with wings... because fuck you, they're cute.)
- if the story has elves, elves are ALWAYS the oldest race. Humans are always the youngest and weakest race, making up for it with technology or sheer breeding power
- magic systems that always seem to have very strictly designed spells; why is it that nobody ever looks at a spell and thinks "hey, if I did a little of this and a little of that, changed this, BAM! Now I've got a spell that does this other thing instead!" I mean, hey, I loved playing Dungeons and Dragons back in the day too, but TBH, the magic system sucks. Terribly. It needs to be highly regimented and quantified to make it easier for you to just look at a list of spells and roll a few dice. Your book doesn't have dice (although that might be interesting idea for a Choose Your Own Story?) so you should be taking into account that your mages have BRAINS and are going to get creative. If they aren't getting creative, YOU aren't getting creative, and as an author you NEED to be creative. This trope is made 10x worse when your main character's defining "cool factor" is that they are somehow the ONLY creative mage... if a random mage in your story can't eventually figure out how to turn a fireball spell into a flaming sword spell, then your magic system probably sucks. (you can probably tell by now that this is in my top 3 most hated)
Science Fiction:
- translators that can translate languages that they haven't encountered before. As someone who speaks 3 languages (English, French, Japanese) and last girlfriend was a professional translator who spoke 4 languages (Brazilian Portuguese, Spanish, Japanese, English)......shit don't work like that. Even if your fancy translator is able to do the process faster than a human, it still needs reference points. Which means that it will take time and exposure to that language before your translation device will have a sufficient database to begin making ANY sense out of the language. And hand-waving it as "reading the other party's mind" is lazy writing, because you're ignoring the fact that an alien life-form won't necessarily have recognizable thought patterns.
- anachronistic weapons. seriously. show me WHY your character chooses to use a high-carbon-steel broadsword to fight laser-pistol wielding aliens, and make it something interesting besides "the hero always uses a sword" (I hate to admit that even though I can't stand this trope, one of my favorite sci-fi RPG series is Star Ocean, which is pretty much a defining example of the trope)
- space battles that take place on a horizontal plane or treat tactics that aren't on the horizontal as revolutionary. THERE IS NO UP OR DOWN IN SPACE. (Bio of a Space Tyrant is an especially frustrating example of this)
In general:
- the Big Bad presented as having a wide-reaching influence and yet everything bad they do is within the hero's sphere of influence; or the hero somehow ALWAYS happens to be present for everything significant. If you are going to imply that your Big Bad has lots of power over an organization/nation/world, you need to PORTRAY that power, by building a sense of scope through off-screen events that are at least as or more significant than the ones the heroes interfere with. Not to be mean, but if your evil emperor is so pathetic that a bumbling farmboy can manage to interfere with EVERY SINGLE ONE of his evil plots, then your plot sucks. Even if the bumbling farmboy has some special power, he can't simultaneously be all over the empire that the evil emperor rules. And if it's an evil emperor, then by default, bad things will be happening in every corner of the empire. The greater the scope of power of your Big Bad, the more you need to have bad things happening off-screen to show the extent of their power. (this is in my top 3 for sure...)