I know a person who constantly introduces or accentuates the negative
in conversation and despite my protests keeps it up on an ongoing basis.  

This person will remain nameless, but could be called "Negative Nellie". 

Do you know or have such a person in your life?  If so, how do you deal with the stream of negativity?

My approach is to attempt to shut it down as soon as it is incoming. I even rudely interrupt. Anything to stop the stream.  

At this point in life I only want to hear and know the good and positive and, thankfully, there is a lot if you make room for it.  Accentuate the positive and let the sun shine in!

Just call me Half Full Freddie :)