Die Hard 

Bruce Willis cemented his status as an action star portraying hero cop John McClane. As he is playing cat-and-mouse with bad guy Hans Gruber, the villain asks him if he thinks he stands a chance against them. 

Willis was supposed to say a different curse world and instead responded, ‘”Yippee-ki-yay motherf—er!” The crew was nervous that it wouldn’t make it through the first screen testing, but everyone loved it.  The line became McClane’s signature catchphrase throughout the series.