costars and real life BFFs Jennifer Aniston and Lisa Kudrow appeared on ABC's to compete in his celebrity swear off competition.

"If you're faint of heart, I'd like to ask you to cover your ears," Kimmel warned viewers.

The rules were simple. Each contestant had up to five seconds to come up with a curse word without repeating one. Variations were allowed, and after each word, they were asked to hit the reset button.

Aniston and Kudrow managed to out do each other in every round, shouting words and phrases like "c--k sucker," "holy f--k balls," "f--king s--t," "schmuck," "a--wipe," "f--king cock" and "undercarriage eater."

Aniston got creative at one point by using a Greek curse word "Mala*ka". Kudrow, meanwhile, apologised after uttering the phrase "stupid b*tch."

Watch them swear off each other in the video, please click HERE