GEL has a point. I've found myself "shutting down" totally. Walking away a few steps at least, changing topics, ANYTHING to get the negativity to stop. It does. If the topic needs further addressing, pick up a positive approach, "What if we do XYZ" type thing and totally forget the other input. Sometimes things end in a smile atleast.
Pity me that the heart is slow to learn
What the swift mind beholds at every turn.
Edna St. Vincent Millay