How about I have a pretty gross habit? Not many people know about it.
Is your habit hurting you or someone else?
No, it's just pretty gross.
It's alright to have some bad habits as long as they aren't negatively affecting your or anyone else's life. You don't have to tell anyone about your personal habits if you don't want to because it isn't any of their business.
What if I wanted to?
If you want to share a gross habit that you have, it would be best to do so when you are certain a person wants to know about it. Just remember you don't have to share every detail about yourself with others.