(Ex: Busy sidebars, too bright colors, music in the background)
My biggest design pet peeve is sidebar images that aren't properly aligned. Fortunately, I don't see this as much as I used to when I first started blogging years ago. My other pet peeve is not being able to find a search box. It's not something that I use often when I visit other blogs, but there has been several times that I've wanted to search for a specific post, like an author interview, and I can't find a search box. In my opinion, it's a must-have when you're designing your blog layout.
What about you? Do you have any design pet peeves?