Parashat Kedoshim April 24, 2015:

"Do not curse the deaf or put a stumbling block before the blind." Leviticus 19:14
It is taught: Rabbi Natan says, where do we learn that a person should not extend a cup of wine to a Nazirite (who has taken an oath not to drink wine) or a limb taken from a living animal to a Noahite? The Torah commands, "Do not put a stumbling block before the blind." (Babylonia Talmud, Pesahim 22b)
Did your mom (sorry for picking on moms) ever insist that your table guest, whom mom knew to be on a diet, eat more? "Stumbling block before the blind."
Did you ever see a salesman offer a product s/he knew the buyer ought not afford? "Stumbling block before the blind."
Have you ever knowingly offered a drink to an alcoholic? "Stumbling block before the blind."
Jews are biblically and talmudically prohibited from enticing a person into something the speaker knows to be bad for the listener. Notice that one example above is a Jew, and one a gentile. This commandment extends to how we treat both.

Have you ever accepted a compliment for something you knew you didn't do? "Stumbling block before the blind."
We curse the deaf and put stumbling blocks before the blind often in our culture, where watching others fail is too often an art form. Someone I know ran into another person we both know. The person gave the second person a big hello! When the second person came over to talk, having been greeted with elaborate friendship, the first person launched into an unexpected and highly impolite personal criticism of something the first person assumed the second person had done! "Cursing the deaf."
I often have observed people setting verbal traps for people they know, hoping the victim will feel inferior or bad about him/herself. The method is simple: say something that will encourage the victim to let down their guard (cursing the deaf), then say something socially insulting as a surprise.
There's something referred to as "Kansas City nice." It's when a person says nice things to you in polite company, then talks about you in private in uncomplimentary terms. "Cursing the deaf."
Jewish law's intention is to create a civil society, one in which each human being is treated as the very "image of God." Would you curse the image of God? No, of course not. Then why do we say things to hurt the feelings of those around us?

Often I hear people criticize the minutiae of Jewish law. But there's a reason Jewish law is so detailed. It's because life is so detailed. Each moment, each action, makes a difference.

"Who is the person who is eager for life, who desires years of good fortune?
Guard your tongue from evil, and your lips from deceitful speech.Shun evil and do good, seek amity and pursue it." Psalms 34:13-14.