I have a friend. We tell each other everything. We started joking around. Is it right if he sent a picture of his penis as a dare or joke to me? He lives countries away, though.
"But fornication and all uncleanness or covetousness, let it not even be named among you, as is fitting for saints; neither filthiness, nor foolish talking, nor coarse jesting, which are not fitting, but rather giving of thanks. For this you know, that no fornicator, unclean person, nor covetous man, who is an idolater, has any inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not be partakers with them" (Ephesians 5:3-7).
Most people understand that having sex without being married is wrong and that fornication and the acts that lead up to fornication should not be connected with Christians. But if the behaviors are wrong, then it also means that Christians should not talk as if those behaviors are acceptable, even as a part of a joke.
Filthiness is dirty or inappropriate talk. A boy should not be talking about his genitals with a girl he isn't married to and a girl should not be talking about her private parts with a boy she is not married to.
Foolish talk is dumb, worthless discussions. Thus, discussions about bodily functions would fall into this category. Talking about things that are disgusting and have no value to you isn't worth your time.
Coarse jesting is making jokes about sexual matters.
If you, as a Christian, are against fornication, then why talk about it or joke about it? It doesn't matter that you live far from each other, it still gives the wrong impression about what you accept. That is why Paul warned, "Let no one deceive you with empty words."