At the Blu Gorilla tattoo shop, Friday the 13th means two things: cheap tattoos and a line out the door.

Every time the ominous date rolls around, the long-running establishment charges $13 or $31, depending on the size, for pieces of "flash" — simple designs that come on traceable sheets.

Customers can't even see the sheets until they make it in the front door, and there's no time for fancy custom jobs. You point to what you want, then lie down and grit your teeth.

"The line gets longer every year," said tattoo artist Matt Crary, hunched over one of the day's first customers.

Doors opened at 11 a.m. Friday, but people started lining up outside at 6. They came with their parents, classmates, or their ride-or-die friends to score a bargain-basement deal.

Like Black Friday at shopping malls, Friday the 13th is a big day for some tattoo shops. Popularized by Dallas tattoo artist Oliver Peck in the mid-1990s, the tradition of Friday the 13th sales has spread across the country.

At Blu Gorilla, just north of downtown Charleston on Meeting Street Road, a crowd of well over 100 had formed by the time the doors opened. Janice Staley had sent her son-in-law, Robert Timmons, to grab a spot in line at 6:30.

"It's a family affair, you know," Staley said. "I think I'm going to get a diamond. I don't know."

Late arrivals Hayley Durant and Madeline Donoughue walked up sipping iced coffee, unsure of what they would pick once they got inside.

"We do impulse things together," Donoughue said.

The brewery next door, Fatty's Beer Works, saw an opportunity to enliven the mood. Bartender Alex Lester came in to work at 10 a.m. to chop up fruit for folks standing in line, turn on the sound system, and start slinging suds. He had already poured a few pints by 11:30.

Lester was there on the last Friday the 13th in April, and he said some customers got sunburned and surly standing in the heat all day. This time, a gray haze kept the sun from beating down too hard. Some customers planned ahead and brought folding chairs and jugs of water to share.

At Blu Gorilla, Crary figures it costs the shop about $5 in supplies for each tattoo. There's a $7 minimum tip for Friday the 13th customers, so a small tattoo really costs $20 and nets $15 for the shop.

It's not much, but they do some serious volume: The first customer was out the door by 11:10, proudly sporting a pair of tattoos of Rick and Morty from the TV show of the same name.

"It's definitely not super profitable for us," Crary said, "but we're having fun."

Reach Paul Bowers at 843-937-5546. Follow him on Twitter @paul_bowers.