My brother and I used to argue a LOT. Like, all the time. And I admit, being the little sister, I was kind of a pain, and may have tried irritating him sometimes, but after a while we started talking nicer to each other, and now we get along so well, I couldn't tell you the last time we even had an argument. Why? Because we learned to talk to each other kindly instead of every other thing we say being an insult. I'm not saying that we're perfect. Not at all. But if we could be like that to everyone, how easy do you think life would be? This is why we are told to be kind to our enemies. It can be so easy to do nothing but talk bad about people who don't like us or who we don't like. But if we look in 1 Samuel 24:3-5 says, "And he came to the sheepfolds by the way, where there was a cave, and Saul went in to relieve himself. Now David and his men were sitting in the innermost parts of the cave. And the men of David said to him, 'Here is the day of which the Lord said to you, "Behold, I will give your enemy into your hand, and you shall do to him as it shall seem good to you."' And David arose and stealthily cut off a corner of Saul's robe." Okay, so here David is given pretty much free reign to do whatever he wants to Saul who has tried murdering him on several occasions. I don't know about you, but no one has attempted to murder me on several occasions. If David was able to spare Saul's life, even though he knew that Saul was trying to kill him, then I'm sure that we can resist the temptation to kill someone's reputation or friendship with someone.
We were given the ability to speak (or communicate in some way) not so that we could talk bad about people, but so we could build them up, and so that we could drive people TO Christianity. Not away from it. So next time you're talking to someone about someone else, make sure it's in a positive way. Even if they are mean to you, you'll always feel worse about someone when you talk bad about them, so why bother??