God, there's so many good ones.
Let's see...

Alright, Halloween 2005 I threw a party in my basement. There was no smoking during the actual party, just because there's some really good kids who don't drink or do drugs or anything. But after the party, a couple friends stay behind and spend the night. And we smoke a lot.
So I'm high, and I decide to bring down the strobe light, the blacklight, and the glow-in-the-dark ouija board of mine. The board's glowing from the backlight, and the strobe's on the floor.

My friend looks over at the ouija board on the floor and starts FREAKING out. "It's moving! FUCK, dude! It's fucking moving!" And I go over to her, and I'm like, "Dude, don't be rediculous, you're fucking high. The ouija board is NOT moving". But she keeps saying it is. In my attempt to prove it's not, I look over at the ouija board. The strobe is on the ground behind it, creating this illusion that it actually is moving across my floor on it's own.

But I'm too high to think correctly. And I SCREAM when I see it. I scream, hide behind one of those supporting poles in my basement, and wake up my entire family. At one in the morning.
And the other friend just starts laughing her ass off, while Tiffany keeps going "I TOLD you it was fucking moving, man. I told you!"

Never have lived that one down.