Ok, I'm probably showing my age here, but when I was (VERY) young in the mid 1970's, they had these things called mood rings. The idea was the stone (or plastic) would change color depending on your mood. This was one of those fads that took off real big and then died just as quickly. You can read about them on Wikipedia here. My biggest memory of them is that they didn't really work, either they didn't change or they changed randomly.
Today, I see that there is now a cell phone app that can determine your mood. (see here). According to the article, "'EmotionSense' uses speech-recognition software and phone sensors in standard smart phones to assess how people's emotions are influenced by factors such as their surroundings, the time of day, or their relationships with others."
While I was never impressed with the original mood rings, I think this has some real potential. If you could set the ringer on your phone to play different ringtones based on the caller's mood, you would really have a marketable product. Wife calls in a good mood? - Answer right away. Wife calls in a bad mood? - Gee, I'm real busy right now. But I'll get back right away.
Somehow, this brings a new meaning to a "mood ring".