I don't believe that it is possible to turn someone away from God. Each believer has been chosen according to the foreknowledge of God, and even though a person may use an offensive word as an excuse to temporarily run from God, if they belong to Christ, they will not remain in that state.
I Peter 1:1
... who have been chosen according to the foreknowledge of God the Father...
We are not responsible for saving people or for causing anyone to remain in an unsaved state, though we can be negatively influential in that way, causing others to rebel for a period of time. Those who have been given to Christ will come to him. (I reject any calvanist doctrines which may inadvertantly overlap with this post)
Those who will be saved were chosen from the beginning, however this does not mean that Christians won't wound people occassionally, or misrepresent God's nature, from time to time. There are individuals who have been 'legalistically' abused in some church gatherings. Judging by appearence, catoring to the rich, misinterpreting scriptures for the purpose of judging or condemning, are only a few of the ways that some may have caused someone to reject the salvation message temporarily, until God can orchestrate a more fruitful encounter with some other believer or church, that will present Christ in a way they are receptive to. The Kingdom was given to Christ, and this includes every saved soul. Even the ones who aren't yet aware that they will be saved, and Jesus will lose none of them.
John 6:39
... And this is the will of him who sent me, that I shall lose none of all that he has given me, but raise them up at the last day.
The truth is, each of us, including myself, have more than likely been in a position where we have failed to accurately reflect God's character. Perhaps we said something we should not have said, or began witnessing, but ended up debating and arguing with the very person we were trying to save. We serve a forgiving God, and each one of us is growing and learning. Everyone wishes that they could speak specifically into the lives of everyone they meet, but the fact is sometimes we blow it, or we simply sow a seed for someone else to water at a later time.
Words can kill. But they do not kill physically or spiritually, they have the potential to kill a person's passion for life, their motivation, and their sense of worth, and I suppose, in a sense, it is like murder, as these are left wounded and hurting without remedy.
We are not perfect, though we strive for perfection, and our words are not always perfect nuggets of wisdom which roll from our mouths. God keeps a watchful eye on his sheep and he knows how to bring them back, wounded or otherwise. The Holy Spirit is an expert at changing hearts, and restoring bruised people. Let's not beat ourselves up, or condemn our brothers and sisters who may have chased a few sheep, but let us be ready to speak by the Spirit as often as God gives us the privelege of participating in His plan for the salvation of those who are His.