A user interface which, whether by malicious design or incompetence, tends to confuse, annoy, frustrate, or otherwise alienate users. Abbreviated PUI. The canonical example is the UI of Apple's QuickTime 4.0 Player, which became painful by mimicking the Real World.
Here is a short list of some of the faults of the player. (Note that this player breaks many of the rules of the Macintosh Human Interface Guidelines as well.)
- There was no visual cue whether a button could be pressed or not. While a movie was playing, it appeared that the Play button was enabled, and the Stop button was not.
- There was a lot of wasted space in making the player appear to be a size that would be convenient for a handheld device. An object on a screen has no reason to fit one's hand.
- The volume control mimicked a thumbwheel on a real-world device, causing new users to click the bottom, drag to the top, and release; this process would be repeated even though the volume would continue to increase if the mouse moved above the top of the thumbwheel. The PUI gave no hint that such an action was possible.
- Elements that displayed at the bottom of the player, such as the Favorites drawer, the Advanced Controls, and the Information panel competed for screenspace.
- By refusing to use the OS's toolkit, the standard method of resizing or zooming the window was lost. Also, third-party programs that could do useful stuff with the standard window information wouldn't work with it. In short, it does less stuff, and does it worse, than it would have by being standard.
The general principle that designers forget when they create a PUI is that computers aren't reality. Though they can perform functions similar to real objects, they can be much better. A typewriter doesn't have find and replace, but a computer-based word processor does.