Some of the most annoying stuff are:
- Gigantic poorly named methods that don't really reveal what's going on. Methods should be small and named in a way to describe what's happening, like an explanation of what's going on.
- Code from different features in the same place. It slows me down having to deal with code from feature A when I'm fixing feature B. Avoid this.
- Code from one feature in different places. This is probably the most annoying. Having to chase the code from one feature along multiple files and directories can stress me out really bad. People tend to make that mistake in the name of DRY (don't repeat yourself), but completely forget KISS (keep it simple, stupid) in the process. In my experience, KISS is waaaaaaaay more important than DRY.