Lock the Bathroom Door!

At work, there is one bathroom closer to my office than the main bathroom. It's off to the side and a "one-er." I prefer to use this one, mainly just because it's closer so I always walk by it. If it's locked I just make the loop to the main bathroom. Today I walked by it, pulled on the handle, slowly began to open the door, and I hear, "Oh, I'm sorry.." I quickly shut it and kept walking to avoid any unnessary eye contact with the person I nearly walked in on. Luckily, she was already at the sink. Given the orientation of the bathroom, had she been using the restroom, I would have seen the whole show. Now here's my question: Who doesn't lock the door behind them when using the bathroom at work? How can you just forget that one essential component? And like I said, it's a "one-er" so any sex can use it. What if I had been a man walking in on a woman. How awkward.