The Cup of tea is an unobtainable item encountered during Zogre Flesh Eaters. It is found in the room of Sithik Ints in Yanille, but cannot be picked up.
During the quest, the strange potion should be used on the cup of tea to turn Sithik into an ogre, whereupon he reveals the secret to making Relicym's balm and brutal arrows.
If you try to take his cup of tea, he will shout at you to stop. Telekinetic Grab will also not work to pick up the cup of tea, and Sithik will call you a telegrabbing fiend.