Ghostbusters star and Saturday Night Live funnywoman Kate was allowed to improvise a lot of her dialogue for the new festive comedy, which also stars Jennifer Aniston, Jason Bateman, Courtney B. Vance, and T.J. Miller.

However, her witty remarks would often cause Olivia to burst out in laughter, so the X-Men: Apocalypse beauty had to find an unconventional way to curb her giggles.

"I think with Kate, I ruined most takes because I was laughing uncontrollably," Olivia confessed on U.S. breakfast show Good Morning America, "so I didn't know how they were going to shoot it.

"Honestly, I had to take a pen and stab myself under the table... because she was so (hilarious). They just let her run (improvise), like, 'Here, just do whatever you want.'"

Kate ended up having to jokingly scold her co-star to encourage her to quit laughing.

"I was like, 'I'm so sorry!'" Olivia shared.

Despite their fun times onset, both women were pleasantly surprised to discover just how funny the final cut of the movie was, after viewing Office Christmas Party in its entirety at its New York City premiere on Monday night (05Dec16).

"I saw it for the first time last night and I was like, 'This is really really funny!'," Olivia said, "and I was excited because when you do movies, you never know if you're part of something that's like, (genuinely funny)."

"While we were filming it it was like the best time I ever had, it was so chaotic and so fun," Kate added, with Olivia chiming in, "But there's so many pieces you don't get to see because there's all these different scenes, and you put them together and you don't know really what they're going to take."

Office Christmas Party, directed by Josh Gordon and Will Speck, stars Aniston as a company CEO who tries to shut down a wild end-of-year bash at the Chicago, Illinois branch of the firm, run by her brother, played by Miller.

It opens in theatres this week (begs05Dec16).