Here are some tips for avoiding tearing up while cutting onions that I have picked up along the way:
- put the onion in the freezer for a few minutes before cutting as this will reduce the amount of juices that get released;
- chew on a toothpick while cutting; or
- run hot water over the knife before and during cutting.

You can find out why onions bring tears to our eyes from this short, but informative, page from the U.S. Library of Congress.

Anyone else have any other tips?