There is an EXCELLENT book on the market titled "Words That Hurt, Words That Heal" It's written by Rabbi Joseph Teluskin. He talks about words and how those words absolutely affect people. The two examples that most stick out in my mind is the dinner party that someone spent weeks planning and executing. Then the guest says "oh did you notice the dirty bathroom?" That is so awful and hurtful.
The other example that really stuck in my mind...even if you really like someone, if you speak of that person in the company of someone who does not care for the person, you actually end up putting the person in an uncomfortable situation as they don't share your enthusiasm for the person. Interesting concept huh?