Dear unknown pen pirate,
I am sorry. You were probably unaware that the pen you (perhaps accidentally) "acquired" was my favorite of all favorites. Undoubtably, you were unaware of the great significance of this particular quill. You surely had no knowledge that it is one-of-a-kind in my potpourri of utensils.
Please let me inform you that the instrument now in your possession is of utmost value to me. I urge you to immediately reinstate this item to it's original place (my desk)... if done so within 48 hours, no questions will be asked, and no charges will be pressed.
IF you choose to ignore this warning and urging to recompense, be assured that your conscience shall surely convict you immeasurably and may your mind be consumed and overcome with incomparable guilt!
Devoted Pen Collector Extraordinaire