Paul spoke already of "cleaning house." Getting rid of those past behaviors that don't belong in a Christian's life. Here he is emphasizing that what the world calls "a laugh" is not funny in the eyes of God. The book of Proverbs makes it very clear that this kind of language is only used by fools and ignorant people who belittle themselves when they speak. A Christian is not to engage in such speech.
Instead, a believer should be full of "thankfulness to God." There is ALWAYS so much to be thankful for, even in the worst of times. For a believer, "from the rising of the sun to the going down of the same, the name of the Lord should be praised." Psalm 113:3. Thankfulness in the believer's heart and expressed on the believers tongue never allows unseemly talk to be the believer's language. Remember Psalm 103:2, "Bless the Lord, O my soul, and forget not all His benefits." The more we "count our blessings" the more our tongue will be singing God's praise and giving Him thanks.
Now, be thankful in public!! Let those around you know that God has blessed your life and you're not ashamed to say so! Your thankfulness to the Lord will be a refreshing sound in the ears of those who hear you!