I don't nag anyone ever. If you don't do what I want, fine. Do what you want. Don't even try to nag me. I was nagged on a daily basis by my mother. I don't even hear it.
Of course you don't rag them. That's just plain rude.
However, there are times when you cannot leave it alone entirely. For example, if a person you care about has a very old animal that means a lot to them (they love dearly), they may become blind to the fact that it no longer has quality of life (it's suffering). You don't rag on them about it, but for the sake of the animal, you shouldn't simply "leave it alone" either. One must use their better judgement - especially when it concerns someone who means a lot to you.
There is a part that's missing in the question Shuhak. I meant to add that it means absolutely nothing to you in fact you think it is ridiculous! Say for example you were an agnostic and never attended church but you couldn't commit to being an Atheist because you wanted to leave that door open "just in case" and you loved someone who was very devout and sincerely religious. You would avoid the subject right and respect the person enough to withhold any putdown comments. You can think whatever you like about whatever you like and still be polite and kind and caring of the person you love or like a lot. Also if folks are very sensitive about something and you care for them it is unkind to keep pushing on that sensitivity for no reason. Thank you for your thoughtful reply. Does my clarifying my intention change anything for you? Oh and I do very much like the animal inclusion. That is a definite kindness and caring. Sometimes we can't see what is right in front of us and it's a blessing to have someone who is in our corner to show us! ;)
Shuhak 