Say what you mean, and mean what you say. Orrrr...go the passive aggressive route and leave this Up Yours mug on your co-worker's desk when he and the rest of your team are in a meeting and you're sure no one else will see that it's you who put it there. Makes a swell White Elephant gift too!
Again, as long as your name isn't attached to it.
The Up Yours mug is pretty self-explanatory. White ceramic on the outside, white ceramic on the inside, and...surprise when the coffee's gone!...white ceramic 3D fist flipping the bird rising up out of the mug's interior base.