Here are a few web design features that irritate if not infuriate me. I suspect that other netizens feel the same way, and have no idea why web designers persist in using them.
1. Auto-playing sound
Whenever I open up a website and sound starts blasting out of speakers, you make me want to beat you with a stick. I know what a play button looks like. If I want to listen to your screeching, I'll click on it. Until then, shut up. Example
2. Flash intro
No one cares about your crappy 5-second animation that takes 30 seconds to load and delays my entry into the actual content of your website. It's bad for you, too, as some search engines are confused by Flash introductions and won't index your content into search results. Example (warning: auto-playing sound effects, followed by stick beating)
3. Expanding ads
I get it: web hosting costs money, and you may want to turn a profit as well cover costs. Feel free to create huge banner and sidebar ads. Make them as big as you want -- so as long as they don't suddenly take over the screen when I hover the mouse over some seemingly-innocuous spot. And if your expanding ad plays a video, or worse, sound, then it won't be a stick that I'll beat you with. Example
4. Slideshows with one picture per page
Again, web hosting costs money. But up big ads -- as big as you want. But making me load a new page every single f&%$ing time I look at a picture does nothing but makes me less likely to visit your advertisers. Example
There are other bad website design practices. Many of these have been largely eliminated by custom (e.g. sideways scrolling, linkjacking) or technology (e.g. pop-up ads). But these are the ones that make me hate your website.
What would you, dear readers, add to the list?