1. Place some of your content in a small frame and force your visitors to read the content through that small window. Don't worry about what constitutes as "small" here, since usually, even if you make a big frame, it'll be too small by most visitors. This thing has a high irritation value since your visitors have to view the information through that small little box and scroll continuously to see the text while the rest of the browser window is filled with information they don't really want to read. With this strategy, visitors cannot resize or maximize the window to make their reading more efficient or pleasurable. This method will allow you to frustrate those hapless souls and, as a bonus, make them leave your site.
2. Disable the right click menu of the browser. Nevermind that people need the right click menu for many purposes, and that they can access the same functions through the main menu bar even after you've disabled it. After all, if your aim is to annoy, you might as well make their visit to your site as unpleasant as possible.
3. Play background music when they arrive at your page. If that's not enough of an annoyance, make sure you loop the music so that your visitors are plagued by it continuously while they are on your page. If you're feeling particularly sadistic, place automatically-playing music on many (or even all) pages of your site. You don't have to worry about choosing a horrible tune — choose your favorite piece if you like. Since one man's meat is another man's poison, any sort of music tends to annoy most visitors.
4. Make every link on your site open in a new window when your visitor clicks on it. That is, put a target="_blank" to every link. This will annoy visitors since every time they click on a link in your site, a new window or tab will open. Imagine the number of windows those poor sods will find open on their computer if they try to read every page of your 100-page site. Delicious, isn't it? Another benefit of this technique is that it makes your site look amateurish.
5. Force your visitors to navigate your website using Flash. That is, place all your content in a Flash file — text, pictures, links, etc — even if Flash is not ideal for such content (a straight HTML page is best for those types of content). Make sure that visitors who don't have the Flash plugin enabled or installed cannot see anything or do much on your website. This effectively drives away all mobile users, a group of users that is growing in size, as well as cripple your visitors who have come to expect certain facilities to always be available in their browsers (such as the BACK key, the ability to bookmark specific pages, the ability to open certain links in a new tab, etc) when they visit websites. Now they will be forced to work through the more limited Flash plugin of their browser with whatever subset of features you deign to provide. In fact, exclusively using Flash for your site content might even help you to drop to the bottom of search engine listings too, thereby reducing the number of visitors to your site. After all, if you don't have visitors, you don't have to think of new ways to annoy them.
All in all, webmasters are prone to making mistakes. However, with this comprehensive guide, they don't have to. Websites should be as easy to read as possible. With these common mistakes out of the way, that goal should be more plausible.