Be ye therefore followers of God, as dear children;
 And walk in love, as Christ also hath loved us, and hath given himself for us an offering and a sacrifice to God for a sweetsmelling savour.
 But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints;
 Neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks.
The words “becometh” and “convenient” have similar meanings. They refer to that which is fitting, proper, or suitable. In this passage Paul mentions six things that are not fitting, proper, or suitable for a Christian to partake in, and then he mentions something that is: giving thanks. Thanksgiving is an integral part of the Christian walk (Col. 2:6-7). An unthankful Christian is very inconvenient.
In v.4 we are told what kind of talk is not convenient for saints, and the kind that is. The Christian walk is more about what we do than what we don’t do. Upon salvation God took us out of the old man (flesh) and put us in the new man (Body of Christ). By faith we are to practically put off the deeds of old man and put on the deeds of the new man in our daily walk (Eph. 4:22-24). This should show up in our words (Eph. 4:25, 29).
Corrupt communication comes from a corrupt heart (Eph. 4:22; Matt. 12:33-35). Murmuring and complaining qualify as corrupt communication and foolish talking (Num. 11:1). In light of all God had done for Israel, how foolish it was for them to complain about anything! Their murmuring spread like a disease (1 Cor. 10:10). What about us? God has done even more for the Body of Christ! We should do all things without murmuring (Phil. 2:12-16). Murmuring is the opposite of thanksgiving. Jesting is also corrupt communication. It has to do with telling stories for the purpose of diversion and merriment. Much of what is called preaching today is full of jesting. Bad doctrine is also corrupt communication (1 Cor. 15:33; Titus 2:7-8).
Thankfulness is a mark of true spirituality (Eph. 5:18-21). In light of ALL that God has done for us (Eph. 1-3), it is convenient for us to constantly be giving Him thanks both privately (Phil. 4:6; Col. 4:2) and publicly (1 Cor. 14:16-17).
It is possible to verbally give thanks without being thankful. Real thanksgiving comes from a thankful heart (Col. 3:15-17). Paul referred to being thankful about 40 times in his 13 epistles. He is our pattern. We should be giving thanks specifically, sincerely, and continually (1 Thess. 5:18).