halacha - Is it a sin to joke about sinning?

For instance, to joke about committing suicide or something less extreme like eating non-kosher.

My inclination is towards saying that it is forbidden since it might desensitize one to the idea itself, even if only by a small amount. However, I have no sources on the matter, which is why I ask.

Edit: To clarify, I'm strictly talking about a spoken joke, not a practical one.