As we know, the main purpose of a coaster on the desk is to display a nice picture (well, until someone's wife should accidentally spill nail polish remover on it...). And, of course, in the late 90's, they had a secondary purpose, which was to provide a use for all those millions of 'free' AOL discs that were being sent out everywhere.
But the other use of a coaster, one that is seldom worthy of mention, is to prevent coffee rings from appearing on furniture. See, the coffee ring forms on the coaster instead, thus sparing the shame of having beringed furniture. It's an important, if seldom-acknowledged, job.
Except that what happened this morning was that the coffee ring formed on the coaster, the coaster then attached itself to the mug (damn you, surface tension!), and then when the mug was lifted the coaster leapt to freedom, presumably to start a new life as a paratrooper, fell to the desk, landed face-down, and transferred a wonderfully neat coffee ring to the very surface it was supposed to be protecting!
In other news - I'm now back at work for the year. It has been good so far.