If your boss is that person, odds are they e already noticed that person who is always out the 2nd Monday of the month. It could be legit. But if you bring it up again, be prepared to be hit with something along the lines of: maybe you need to more to do if you have all this time to keep up with the comings and goings of a colleague. But kudos to you for owning the karmic retribution!! Hope you feel better!