Oh man, my site falls under some of the categories mentioned here.
I agree with a lot of points and I will consider everyone's opinions while working!
My sins: 1)
JavaScript as Foundation: My site requires a browser with JavaScript enabled or otherwise it will not work at all. That is due to some "shortcuts" I have taken while coding. I would have used PHP instead if Neocities supported it.
2)
Not Sharing Buttons: I am one of those who showcase their 88x31 buttons but have not linked anyone else back in return. That is because I have yet to make an "external links" page! I have gathered a lot of buttons from others and I really want to add them some time. ^^
3)
Screen Adaptability: Thanks to my wonky CSS skill set, my site sometimes works on smaller screens and mobiles... and sometimes it doesn't.
My pet-peeves: 1)
Autoplay: I also have an issue with autoplay, especially if there have not been any warnings prior and the sound is very loud and sudden. I get spooked!
2)
Text Size: I refuse to read tiny text for my eyes' sake. :P
3)
Pop-ups: While browser pop-ups might be informative, I find them quite annoying. I have come across instances where pop-ups were used as warnings on index/home pages, which were useful at first, but became a bit frustrating to deal with once you have to load/visit the page over and over again.
4)
Dead Ends: Unfinished pages or links that get you into 404 pages, especially without an indicator. I do not have a problem in most scenarios, unless the entire site consists of non-existent, "Under Construction" or "Work In Progress" pages.
Stuff I do not mind that much: 1)
Carrd-like Sites: It's their site. I cannot tell them what to do. Though, I have got to admit that it takes the fun out of web creation if the code is copy+pasted. If they made it themselves, sure! I don't care!
2)
No Meat, Just Decoration: I do not mind seeing sites that are just aesthetic without much context to rely on. I think they are really beautiful in some cases. It is a different approach to most common personal sites. Again, they can do whatever they want with their site.
These are some subjects I could think about for now.