Movie sets aren't like ordinary workplaces.

For months on end, actors spend every waking moment working together, eating together, and living next to each other in cramped trailers.

It's no wonder then that co-stars fall in love and increasingly often, get matching tattoos to celebrate their lifelong friendships (until perhaps the movie bombs).

After the cast of supervilain flick Suicide Squad were spotted inking each other with matching tattoos, we had a look at famous cast mates who immortalised their bonds.

Suicide Squad

On Wednesday, cast members of the DC comic fim were snapped inking each other with wonky and mismatched tattoos which read "skwad".

Director David Ayer tweeted a photo of Margot Robbie tattooing his forearm, while Swedish actor Joel Kinnaman bravely offered his bicep up to Will Smith.

"Will has many many talents, tattooing is not one of them. It was like watching a drunk baby fly a helicopter," Kinnaman wrote on Instagram.

Australian actor Jai Courtney also shared a photo of his new "skwad" tattoo.

The Lord of the Rings

The cast of J. R. R. Tolkien fantasy The Lord of the Rings were perhaps the earliest adoptees of the matching cast mate tattoo craze. 

Before shooting finished on the final film, eight of the nine members of the film's fellowship got matching tattoos of the word "nine" spelled out in the Elvish script created by Tolkien.

Orlando Bloom, Elijah Wood, Dominic Monaghan, Sean Bean, Viggo Mortensen, Ian McKellen, Billy Boyd and Sean Astin all got inked in various parts of their bodies, but the ninth member, John Rhys-Davies, declined and sent his stunt double instead.

Director Peter Jackson also got a tattoo of the number "ten".

Breaking Bad

Was there a better acting bromance than that of the one between Breaking Bad actors Bryan Cranston and Aaron Paul?

On the last day of filming, Cranston, Paul and other cast and crew members were having farewell drinks when they decided to get inked by a set decorator who was also a tattoo artist.

Cranston got the show's logo tattooed on his finger, while Paul got the name of an episode tattooed on his bicep. Other members also reportedly got Breaking Bad-themed tatts.

"It seemed appropriate. I mean, Breaking Bad changed my life," Cranston told GQ of the Emmy Award-winning show.

Harry Potter

One of the most famous casts in the world, the members of the Harry Potter film franchise discussed marking the end of the experience with matching lightning bolt tattoos, but ultimately decided against it.

"There was talk between us about doing something like a tattoo," Rupert Grint said it an interview with Daily Mirror.

"It would have been something subtle like Harry's lightning scar. It would've been a great way of marking the end of filming."

Apparently Emma Watson also wanted to celebrate the end of filming, but ruled out getting a tattoo.

Mad Max

Mad Max actors have described the blockbuster's intense filming process where they spent five months on location in the Namibian dessert with no reception.

Australian actress Courtney Eaton played one of the sister-brides of villain Immortan Joe.

In May she revealed she and her sister-bride cast mates Riley Keough, Zoe Kravitz, Abbey Lee Kershaw and Rosie Huntington-Whiteley got matching tattoos.

"We all got the same tattoo—three little dots and a triangle," Eaton told Vanity Fair.