My husband has a theory that when it comes to bathrooms, people are either knockers or lockers.
The knockers do not take anything for granted. They assume that if a door is closed, someone might be in there. These are the more considerate people of the world. They knock, just in case. Although most of them probably lock, they do not assume that everyone does. The last thing they want is to walk in on someone.
The lockers assume that everyone else is a locker. They think that everyone should be a locker. They are armed with the mission to walk in on people to force them into becoming lockers as well. If there is someone in there they do not want to talk to them. They hate when knockers knock and they have to answer them. Try the door - if it is locked - go away and don't bother me.
Then I think there is a third group - the never-lockers. They assume that everyone is a knocker. They never lock a door (you are lucky if they shut it) and become quite indignant if they are walked in on.
I wasn't aware of the locker/knocker/never-locker camps until we put in a new bathroom. T wants a door that locks. After pricing the locking, historically accurate locking door hardware (they are called privacy knobs by the way) I was questioning the need to lock yourself into a bathroom in your own home. With kids it just leads to the possibility of them locking themselves in. I was under the crazy impression that if the door was shut most people would knock.
Well, we had our first test of the new bathroom during a family party a few weeks ago. T's Mother was happy to not have to go upstairs. Her question after "does the plumbing work" was "does the door lock?". I said no, but it does shut (and we do have a door)...and then I thought "so that's where he gets it from".
While she was using the bathroom, two of her grandchildren walked in on her!!! Apparently my nieces and nephews are all lockers. Now that we have determined that most of my husband's side of the family are lockers, I guess we do need a lock, otherwise they will be walking in on everyone.
Still, I am thinking of a simple hook and eye or sliding bolt like Amy suggested. Simple, cheap and should keep the lockers out.
Here is the test:
The next time you are using a bathroom facility that is not inside your own home (rules tend change at home) and the door is shut - what do you do? If you knock, well yup you are a knocker. If you try the knob to see if it is locked (if locked you walk away and if not you open and see if anyone yells) you are a locker. I you never lock a bathroom door no matter where you are, you are a never-locker...