When you watch a movie or TV show, chemistry is always important. You want to really believe the people on your screen are friends, partners, siblings, whatever. For the most part, this chemistry comes across on screen because in real life the bond was just as close.

However, some of the best on-screen duos didn't actually get along on set, which makes their chemistry that much more impressive!

Here are some co-stars who had a hate on for each other. Were you able to tell?

1. Patrick Swayze and Jennifer Grey, Dirty Dancing

Swayze recalled working with Grey in his memoir, admitting he didn't have the patience for her antics and constant goofing around. In his opinion, she wasted too many takes by goofing off. In the teaching montage, you can see Grey laughing and Swayze looking annoyed. That wasn't acting. It was a real moment from the set.

2. Gillian Anderson and David Duchovny, The X-Files

"Familiarity breeds contempt," Duchovny stated. "We used to argue about nothing. We couldn't stand the sight of each other."

3. Rachel McAdams and Ryan Gosling, The Notebook

Though they ended up dating in real life, McAdams and Gosling both admit to having bickered and fought throughout the filming of The Notebook.

4. Leonardo DiCaprio and Clare Danes, Romeo and Juliet

Danes was not shy about her disdain for her co-star, calling DiCaprio "very immature." Sources from the set say the two were never close unless it was necessary for filming.

5. Sarah Jessica Parker and Kim Cattrall, Sex and the City

This was a case of jealousy between Parker and Cattrall. Sources say Parker was jealous that Cattrall's character was the fan favorite and started getting more screen time, while Cattrall was jealous that Parker was getting paid double what everyone else was.

6. Jennie Garth and Shannen Doherty, Beverly Hills 90210

"There were times when we loved each other and there were times when we wanted to claw each other's eyes out," Garth said. "It was more of just young girls finding their way and finding their individual voices. Shannen and I are both Aries women, we're both very strong, independent women, so we butt heads a lot," she added. "Now, as grown women, we happen to get along as well."

7. Will Smith and Janet Hubert, Fresh Prince of Bel-Air

Hubert was the original Aunt Viv, but she was fired pretty darn quick. She called Smith an "egomaniac" and "snotty-nosed punk" which obviously didn't go over well. She refuses to do a reunion until Smith apologizes for firing her, although something tells us that won't be happening.

8. Josh Hartnett and Harrison Ford, Hollywood Homicide

Ford and Hartnett hated each other so much it started to affect filming.

"There were times we would end up just sitting in the car when we were supposed to be doing a scene and neither of us would say anything for like an hour," Hartnett recalled.

9. Nick Nolte and Julia Roberts, I Love Trouble

Roberts says her and Nolte "gave each other a hard time" from the moment they met. She also said Nolte was "completely disgusting." Nolte, who didn't appreciate the comments, said "[Roberts] is not a nice person, everyone knows that."

10. Teri Hatcher and Marcia Cross, Desperate Housewives

Hatcher didn't get along with anyone on set, with Eva Longoria calling her "just a loner." Particularly, Hatcher and Cross butted heads during a photo shoot when Cross was upset that Hatcher was front and center in the shoot.

11. Shia LaBeouf and Tom Hardy, Lawless

LaBeouf and Hardy admit to fighting in between takes. LaBeouf seemed pretty serious about it, while Hardy laughed it off.

12. Naya Rivera and Lea Michele, Glee

Rivera claims Michele "didn't even talk to her" during the final episodes, and it got so bad that Michele actually tried to get Rivera written off the show.

13. Nathan Fillion and Stana Katic, Castle

"Stana Katic and Nathan Fillion completely despise each other," a source told Us Weekly. "They will not speak when they are off set, and this has been going on for seasons now." It apparently got so bad between the co-stars that they had to go to couples counseling!

14. Richard Gere and Debra Winger, An Officer and a Gentleman

Winger was notoriously hard to work with, and Gere learned this first-hand. The two argued constantly on set, and Winger even mentioned filming the movie was the worst experience of her life.

15. Chad Michael Murray and Sophia Bush, One Tree Hill

These two didn't hate each other at first, getting married after two years of dating in 2004. However, just 5 months later it surfaced that Murray cheated on Bush with his House of Wax co-star Paris Hilton. Bush filed for annulment but it wasn't granted, and the two divorced instead. They continued to work together for 5 years after the ordeal.

16. T.R. Knight, Isaiah Washington, and Patrick Dempsey, Grey's Anatomy

Things got a little heated when Washington (center) called Knight (right) a homophobic slur behind his back. Dempsey wasn't having any of that, so he punched Washington leading to an all-out brawl. Washington was then written off the show, with Knight leaving a few seasons later.