I have an interesting question: if a person has a habit that is not in any way sinful, but which nevertheless would be embarrassing to reveal is it a sin to keep it secret? More accurately: is speaking half-truths to do so a “lie” in the normal sense of the word or is it rather a protection of one’s security? For example: if I am asked what I am doing and am doing something which would be potentially embarrassing to reveal, am I required to do so, or is it permitted to begin doing something else discretely and say that you are doing that thing instead?
The important factor here is whether the person asking you has any right to the truth. You don’t need to disclose such information to simply anyone who asks…you may reasonably evade the question or decline to answer…but if a person has a right to know you should be truthful. An example would be a parent of a minor child, who generally has a right to know about all of their children’s hobbies. As an adult child, this right is less clear. Beyond that, there are probably few circumstances in which an adult owes others the right to the truth regarding non-sinful embarrassing hobbies.