Craig Giffen has watched 1986 wastoid classic Heavy Metal Parking Lot roughly a "bazillion times" since the late '90s, he says. Amid the film's 17 minutes of interviews with epically wasted, elegantly mulleted metalheads tailgating before a Judas Priest concert, Giffen began to fixate on small details—like the preponderance of ZZ Top tour shirts among the attendees. "I counted four or five," he says, "and then I started wondering what other shirts were in it."

He decided he would catalog every shirt in the movie. Just having the idea was enough reason to do it.

"I'm what business people would call 'vertically oriented,'" says the Portland amateur computer programmer behind the website the T-Shirts of Heavy Metal Parking Lot. "I'm like, 'This is what we're doing, we're doing it now, don't fucking talk to me until it's done.' Even if it's something that's going to test my relationship, cost me lots of money and drive me insane, let's do it."

Considering half the interview subjects aren't even wearing shirts, you'd figure the job would be easy. But the original movie and the outtakes on the DVD contain about 30,000 individual frames. Giffen scrolled through each one, noting whatever he could make out and uploading the results to a page that looks like it was built using a vintage GeoCities template. (He's a programmer, not a designer.) He finished it just in time for the film's 30th this past May.

For Giffen, just finishing—or getting close enough—is his reward. As for any grand lessons, he says: "My biggest takeaway is that I didn't realize there were so many Harley-Davidson shirts."