Picking your nose in public is VERY tricky, but I'd venture to say we've all done it at one time or another. My dad used to do it in front of us all the time. He did it out of boredom and sometimes from anxiety (coping mechanism). If my dad got to sit somewhere for a prolonged period of time at home, up went the hand to the nose and he'd pick away. He knew better than to do it at church, however.
I'm a teacher and sitting in the back of the room one day waiting for a teacher to finish his lesson, I saw a kid picking his teeth with his fingers, trying to remove food debris.
Taking medication in front of strangers is also weird, I think.
We'd like to think no one notices us when we do these things, but sadly someone always does. As a teacher, I have to be especially careful.