Ever noticed that some people don't really acknowledge you if they're walking to or from a public restroom? What are they ashamed of? Really, people. We all have been in public restrooms, and honestly, there are only a handful of activities that you can do while in a public restroom. We all know what they are, and two of them are activities that EVERYONE does.
So why the shame? Why do these people not return a greeting after exiting the public toilet?
Here's my theory: We, as a species, aren't ready to embrace the "unspeakable" bodily functions of others outside of a joke or a frat party. Honestly, there's nothing to be ashamed of, but we instill this modest and proper behavior into our society. Why? Because it is, and always will be, a dirty little secret.
There is one thing that I know, I'm not ashamed.
Be warned. If you exit a public toilet around me, I will proceed to greet you and/or ask you if you feel better.