I'm really big on reading fics that are reader inserts and/or ones that feature some romantic-fluffy-thing about two characters I ship. I'm a big sap. However, a lot of reader inserts are just...really annoying. I hate when it's SUCH a reader insert that they are like, your (h/c) hair floated in the wind and your (e/c) eyes sparkled and you were wearing a (f/c) top on. Come on! D: A good reader insert doesn't have to worry about filling that info out. Heck, even if it's a nameless character written in the first or second person POV, I'm content. x] It's like...you don't even have to mention those details. At all. The reader's mind will fill in any blanks. x]

Also I like the confession part of it to be...climatic, semi-realistic, and bonus points if it gives me all those warm fuzzies. >w< If they're just like "OMHG I LOVE YOU!" then I just click out of the story. Sometimes.

Another thing about fanfics in general is when the author's notes is full of...chatting. Also, the things detailed in this video.
Mainly I'm just a big fanservice nut and it bugs me when it's too weaboo-like. ._.

Also I agree with the OP when they said they dislike it when all of the opposite gender characters fall in love with the main character. Goes for both males and females. It's too Mary-Sue-like.