Let there be no filthiness nor foolish talk nor crude joking, which are out of place, but instead let there be thanksgiving.
How much filthy, foolish, or crude joking can a person engage in and not break this rule?
giving thanks always and for everything to God the Father in the name of our Lord Jesus Christ,
What does "everything" include? How often is "always"?
do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God.
What is the breadth of meaning of the words "anything" and "everything"? How inclusive are these words meant to be?
It seems that God really wants us to be thankful. Contrariwise, he does not want us to misuse our mouths through filthiness. He does not want us to waste emotional energy on anxiety. The antidote is thankfulness and prayer.
Pretty simple. Now, go and do it, by the grace of God.
I said "simple", not "easy."
Does that mean that one can never tell a joke or laugh? Of course not! It means that a Christian is supposed to be careful about what is turned into a joke and what is said in order to get a laugh.