According to Ephesians 5:4 foolish talking is not proper or becoming for the saints.
Ephesians 5:4 Neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks.
So, what does foolish talking mean?
It means the kind of talk that is senseless, dull, stupid; which is not fit to instruct, profit, edify—the idle chit chat that is so common in the world today. It means that Christians should have their conversations be serious, sensible, sincere and rather giving thanks to God.
Matthew 12:36 But I say unto you, That every idle word that men shall speak, they shall give account thereof in the day of judgment.
Ephesians 4:29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
Matthew 15:11 Not that which goeth into the mouth defileth a man; but that which cometh out of the mouth, this defileth a man.
Proverbs 15:26 The thoughts of the wicked are an abomination to the LORD: but the words of the pure are pleasant words.
Proverbs 10:11 The mouth of a righteous man is a well of life: but violence covereth the mouth of the wicked.
Psalms 34:13 Keep thy tongue from evil, and thy lips from speaking guile.