Does Christ's "forgiveness" give Christians a license to do people dirty?

I have noticed in my life, and others have said the same thing, that the supposedly devout Christians are the ones in the company, or clroom that go aroud knifing everyone in the back and generally doing people dirty. While the supposedly lost people might tend to be more compionate, or decent. That is not to say that you cannot find examples of the opposite. But, from the Christians I have seen, saying cruel things about whoever does not happen to be standing there, spreading lies, and abusing power, I would not care to become a Christian. I believe it is because these people act indiscriminately because they believe themselves immune to punishment by God because of so-called grace.