The practice of drilling a hole in one's skull to somehow make one smarter or more enlightened.

It seems to me that if anybody is dumb enough to drill a hole in their own head in the first place, it probably couldn't do anything but help. But, hey. That might just be crazy talk.

I first heard of this from a bunch of crazy-ass physics majors I knew. They were trying to build a beowulf type system to model some particle physics experiment that was over my head. The computer work was interesting though, so I was trying to get in on it, at least at the fringes.
Picture a bunch of lunatic college kids sitting around a table in a room stacked with old computers, oscilloscopes, and other electronic devices, most of which appear to have been gutted in the late 50's. None of them really know what they are doing, but they're trying. There's Jim, Pat, Rob, and two Mikes, known as Good Mike and Bad Mike. Good Mike and Bad Mike are the jokers. Pat is the intellegent slacker. Rob, from what I can tell, seems to be a regular joe. Jim knows his shit pretty well, and is somewhat in charge. They keep mentioning trepanation, and laughing. Finally I break down and ask what it is.
Good Mike: "Mike, show him."
Bad Mike: (laughs and turns to the computer) "You're gonna love this."
He pulls up a picture of a woman, screaming, with a drill held against her forehead.
Me: "Holy shit."
Pat: "Yeah. We're trying to talk Jim into doing it, since he's our fearless leader."

Later, I looked up trepanation online and learned a bit more. I don't know what happened to those guys. I got caught up in other things, other projects, and never heard if their efforts came to fruition. However, if someday a group of five lunatic physicists takes over the world, and their leader has a hole in his noggin, I won't be too surprised.