The Diskman Manual
This diskman plays regular CDs, mp3s, and video CDs. While its new technology (at least in 2001), the manual and interface is classically bad.
The student who pointed out this manual said "I almost gave up ... lucky that I like puzzles :-) For example - how do you set the Diskman so that it is playing in random mode and using ESP (Electronic Skip Protection)?
Time yourself to see how long it would take you to understand how to do the above task.
Example pointed out by Student Tomas Florian. Commentary written by Saul Greenberg.