Is it sinful? Does the Bible say anything about the issue?
I’ve always been a bit baffled why modern Christians are so sensitive about “inappropriate” topics. As best I can tell, this pious prudery comes from a sloppy exegesis of the following passage:
and there must be no filthiness and silly talk, or coarse jesting, which are not fitting, but rather giving of thanks.
“filthiness” (aischrotés) means “baseness” or someone who lacks moral character.
“silly talk” (mórologia) literally means foolish (moronic) words.
“course jesting” (eutrapelia) means using wit to refer to sexual functions in a rude and irreverent way.
These concepts are contrasted with thankfulness. Does your language indicate that you have an intelligent appreciation for God’s good creation? Or do you come across as an immoral, stupid person who can only manage to crack cynical jokes about body parts?
But this is not to say “dirty” topics are off limits to Christians. It’s all about how you say it.
To illustrate, consider the following examples:
“Your mouth is a cum receptacle for me to masturbate into.”
The above statement indicates a lack of character. It shows no respect for the sexual needs of the woman. It’s supposed to be clever/funny but there’s no point to the joke. It reveals a godless worldview. The statement does nothing to praise the beauty and goodness of sex. In fact, it lowers the act to a meaningless level.
Contrast that with the following expression from Song of Solomon 4:11:
Your lips, my bride, drip honey; Honey and milk are under your tongue
Both expressions could be referring to the same act. But the latter expression is beautiful rather than base. Instead of using cleverness to lower a sexual act to nihilism, it elevates a physical act we might be tempted to think of as meaningless or gross to it’s proper place of beauty and goodness.
But it is “dirty” in the sense that it’s not something you would talk about in the presence of elderly ladies.
But in the proper context, Christians should feel free to invent and use all kinds of sexual metaphors… so long our language indicates that we have understanding and see sex as a good thing!
P.S. It’s also worth noting that the Bible never instructs us to be offended by “course jesting”… only that we are to avoid doing it ourselves.