9. Dwayne Johnson's Ad-Lib Caught Ludacris Completely Off Guard - Fast & Furious 6
Improvisation is absolutely nothing new on a movie set, and often actors going off script can lead to some of the most memorable scenes in the entire process. Usually, this is down to the actor themselves and what they say, but it can also elicit fantastic reactions from their co-stars.
When Dwayne Johnson joined the Fast franchise in the fifth movie, he undoubtedly offered a shot in the arm and helped with the longevity that it enjoys today. Even now, his most iconic scene may be his "big old forehead" line.
When he entered this particular scene, Tyrese Gibson's Roman told Mia to hide her baby oil, to which Rocky replied with his infamous forehead jab. Ludacris, just taking a sip of his drink, was forced into a genuine spit take.
A reaction like this to an actor's improv would usually be confined to the blooper reel. However, it worked perfectly in the scene. It was a funny insult, so why wouldn't the character laugh? Thankfully, Gibson stayed in character and responded, allowing Justin Lin to leave the scene in the final cut.