What makes a believers speech excellent? Certainly, there is a need for Christians to honor God with their speech. That is, not just clean words (Read Eph 4) but words that reflect the heart of God. I don't think that there is a purpose in swearing from the pulpit, certainly there is a decorum that is demanded in public speech. But I have to be honest and tell you that from the time my boys were little we spoke very frankly about our bodies and bodily functions in what, for those little boys, was "bathroom talk". I always made sure that they understood that we were allowed to speak frankly in private. For some reason, christians feel free to say 'crap' but shrink from saying "Sh**". I am not really sure what the difference is- except that decorum demands that we avoid the use of them.
But surely our words must be more than clean. They must be reflective of the faith that resides in our hearts and the love that we have for our Father God. This is more than saying "Praise God" all the time. What seems most important is what we talk about with freinds and strangers. Are we moving people with our speech toward our God? Maybe we should demand some sense of kindness and gentleness in our words as well.
Finally, exaggeration and half truths have no place in our lives. We must be straight talkers and deal in truth. If we endeavor to honor God with our speaking truth, we have the assurance of the Spirit of Truth walking with us.