I first noticed this when I worked at BYU. More often than not, I would walk into the rest room and another female professor there. The thing is that professor was about 70 years old. So, I came to the conclusion that I must have the bladder of, well, you know. I did make myself feel better by figuring out that maybe I only saw her on half of her visits to the restroom!
Well, I've started to see this pattern emerge at my current work place. I have ended up in the restroom with the same coworker up to 3 times in one day. It even got to be so obvious that I had to say something to her. She just laughed.
And, what else is there to do ... but laugh and use the restroom.