best & worst fic tropes?

Well, one trope that always rubs me the wrong way is the Invincible Hero trope, where the hero basically never loses, no matter what. It's one of the reasons why I can't stand protags like Yusei and Yusaku from Yugioh, as they always, ALWAYS win, even when the stakes aren't high (sans flashbacks but those don't really count). I admit I'm guilty of that trope, too, albeit by accident, as I was unaware of myself committing that very same sin when I was writing Psychic Duelist Django until a good friend pointed it out, which woke me up and I started to rework certain aspects before it got put on hold due to other reasons (mainly the franchise itself becoming the massive mess that it is now turning me off from it). But, yeah, whenever I see a protag being basically invincible and having, like, zero flaws or struggles really doesn't sit well with me.

One that's in bit of a grey area for me is the Protagonist-Centered Morality trope. When it's done right it does pretty good, like in Rising of the Shield Hero with Naofumi and the methods he uses to get his Hero job done correctly. They're morally questionable, but given the time period and the fact it brings desired results it's hard to argue against it (especially when compared to the other three Cardinal Stooges and their consistent screw-ups). However, when it's done wrong it's an absolute nightmare, such as how the narrative always took Kagome's side in Inuyasha even when she's in the wrong and Inuyasha is in the right and was never called out on it by anyone. Whenever that trope is used in fiction it can bring mixed results but if it's executed properly it can make for some really engaging work, especially if it creates a unique morality system that fits with the form of fiction.

In terms of romance tropes, I'm very fond of ones like Forbidden Romance, Battle Couples, and Interspecies Relationships, similar to @Torchic W. Pip. In fact, all three tend to be some of my more commonly used romance tropes with my main leads (ie: Celtic and Skye in Chaos Rising are a Shadokor/Druid and Light Elf, respectively, making them use the Interspecies Romance trope combined with Battle Couple, while Django and Tempest in Psychic Duelist Django are a Psykinox and Elemental, respectively, which not only uses the same trope but is also a Forbidden Romance one because Elementals are terrified of Psykinoxes, Tempest being one of the few exceptions due to lacking her species trademark cowardice while also having resentment for her kind, with a dash of Battle Couple since they sometimes do Tag Duels together). And I also like the whole Dating Catwoman trope, where a hero hooks up with a anti-hero/(former) villain, since it creates a unique morality set up and interactions.

That said, a romance trope I feel that gets run right into the ground is the Childhood Romance trope. Yes, having your childhood friend evolve into a lover is nice, but it's a bit overdone nowadays and I've lost interest in it. In that case I do have a personal beef with Childhood Romances since I once had a Childhood Romance that grew quite a bit into my early teen years that came crashing down in the absolute worst way and time possible, souring my opinion on it and leaving me quite bitter toward the person who left me high and dry when I needed her the most. That said, if it's done right then I can accept it, but usually it feels more forced to me, especially if you don't actually see any childhood interactions with the two (which is a big flaw that various Dragon Quest games have, especially if they're trying to force you to take a certain marriage route, simply resorting to "hey, you have a history with this girl so you should marry her no matter what"). In fact, a canceled series I was planning once (I might attempt to revive it, since the idea still tickles my fancy, and I know this forum would love it, plus I still have some of those documents) invoked both a failed version of the Childhood Romance and a successful Dating Catwoman tropes, resulting in a unique dynamic for the main protag.

Those are the ones that come to mind right now as good, bad, and grey area tropes. Execution is the ultimate key for them, as the tropes can be good if they're done correctly. If done right then the tropes can be glorious but if done wrong they can really ruin a good story. That's my two cents.