Proverbs 15:1 (NKJV)
A soft answer turns away wrath, But a harsh word stirs up anger.
Proverbs is a book of wisdom not a book of rules. This one, however, I need to make a rule in my life. This verse does not say that you must give an answer that will let someone off the hook, rather, it describes the manner in which the answer is given, soft.
You understand that a word given harshly only authorizes the other party to react to the manner in which it was given and not to the truth of the word that was spoken. The Bible says to speak the truth in love.
Ephesians 4:29 (NKJV)
Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers.