mithridatize: To render oneself immune to poisons by accustoming one's body to small amounts of them and then gradually increasing the dosage. Could be used metaphorically to describe building up a tolerance to just about anything — from your wife's nagging to the constant hum of the starship Enterprise's engines.
Pliny the Elder tells us that King Mithridates VI of Pontus (along the Black Sea) didn't trust anyone. He eventually murdered his mother (matricide), his sons (filicide), and the sister he had married (sororicide and uxoricide), as well as killing his entire harem (outright homicide) to keep them from falling into enemy hands. He was worried that someone would try to poison him, so he came up with the idea of taking small daily doses of known poisons and then gradually increasing the dosage as his body grew tolerant of them.
Eventually, he got fed up with his son's (real or imagined) treachery and decided to kill himself. How did he try to do it? It wouldn't be a good story unless he tried to poison himself. By that time, he had developed a total immunity to any of the poisons he could find, so it didn't work! In the end, he had someone stab him to death.
A mithridate is the antidote to all poisons. Of course, Pliny the Elder somehow neglected to reveal the ingredients of the mithridate. Although Pliny's story is likely fictitious (or at least exaggerated), it's still an interesting tale.
The most famous case of mithridatization is perhaps that of the Dread Pirate Roberts (aka, Wesley) in The Princess Bride. He was able to defeat the Sicilian in a match of wits because he had mithridatized himself against the effects of iocaine powder.
[Edited for formatting and some embarrassing spelling errors, 11/20/09.]