For by your words you will be acquitted, and by your words you will be condemned.
All of have said some nasty things at some point in our lives. Fallen people that we are it's difficult for us to live up to the exacting standards of Christ. In the verses prior to this the Lord clearly tells us what the unforgivable sin or blasphemy is. It's rejecting the grace of God and resisting the Holy Spirit. We may stumble and say ungodly words which are forgiven as long as we repent and say "Jesus Christ is Lord."