Question: A man went to a party and drank some of the punch. He then left early. Everyone else at the party who drank the punch subsequently died of poisoning. Why did the man not die?
Answer: The poison was in the ICE and as the ice melted, it poisoned the punch and the man that didn't die left before the ice melted.

Other "Technically Correct" Answers:
1. The punch wasn't poisoned, the food was, which he did not have.
2. He placed the poison in the punch.
3. Someone else placed poison in the punch after he took some.
4. He had a natural immunity to the poison, leading Scully to conclude he was a medical anomaly, and Mulder to conclude he was an alien.
5. The others didn't actually die of poisoning, but at the hands of the Medallin drug cartel, according to Johnnie Cochrane.
6. The dead victims were simply part of a vast right wing conspiracy.
7. He was the only one who didn't know there was a starship in back of the comet the night of the party.
8. He did die, but then lied about it. That was wrong, and for that, he apologized to his family, his nation, and Monica Lewinsky. Now it's time to get back to work on the issues Americans really care about.
9. No one dies of poison anymore, as glam rock has been out of fashion since the late 1980's.
10. He was Professor Plum.

List written by John "Undercard" Doe.