Over me lifetime, mental health and psychiatry have emerged from the shadows and into mainstream media. From Dr. Melfi in The Sopranos to Hannibal Lechter in the Silence of the Lambs series to Gabriel Byrne in In Treatment on HBO, people are being exposed to the concepts and the terminology of psychiatry.
Overall, I think this is a good thing. I believe that education about psychiatry and psychiatric illness will ultimately make appropriate treatment more accessible to us all.
However, along with the greater visibility comes the natural adoption of certain psychiatric terminology into mainstream language. Psychiatry is especially susceptible to this because our technical terms can sound like everyday emotions that people are familiar with (depression, anxiety) or descriptive in such a way that people think they understand what the words refer to (bipolar, obsessive-compulsive). The problem is that people's impressions of what the words mean are not always correct. For a field in which stigma and irrational fear is a hallmark, this can create serious problems.
I am not about to tell people what words they can and cannot use, but I am hoping that people will think carefully about what certain labels mean depending on where they originate. You can refer to your moody neighbor as seeming "bipolar" but understand that this does not mean that he necessarily has a mental illness or needs to be put on medications (though you might want him to be evaluated)