When you speak ill of others, consider that it hurts you more than it hurts them. This is because your unkind thoughts are the loudest within you. All of your thoughts arise within your mind. Some may flow out into the world in the words you speak or use. These thoughts are at their highest intensity within you.
No matter what situation you are in or how hurt you are, you do not need to have the last word or symbolically win the argument. If you are angry, annoyed or otherwise emotional, you may find that your last words can often obliterate good intentions or even the good memories.
Try to catch any unkind thoughts before they become expressed out into the world; pause, then ask yourself do you really want to be this way. Pausing will help to break the cycle of your conditional reactions, allowing you to change your thoughts to those which you will not later regret.