Screenrant:
Much to the dismay of screenwriters, movies scripts aren't always set in stone. They are often like living objects constantly evolving during the filming process. Some films, like Jaws and Annie Hall, don't even have a finished script when the cameras start to roll.
Actors and actresses are regularly ad libbing, improvising or going off-script while reciting their lines. Sometimes the directors hate it - other times they love it. Occasionally the improved lines become immortalized as some of the most memorable in cinema history.
Some classic scenes in this list. Had no idea many of them were unscripted. Kudos to the author for a great post idea!
Haha Zoolander great movie as the other movies on the list.
Bill Murray, one of my favorite actors ever, all his movies are epic.
One of the best is from Goodfellas when the trio(Pesci, Liotta, and De Niro) are at the table (after they whack Billy Batts) and the only thing they have to mention is the painting. The entire scene is ad libbed!
I got your name I got your ass you will not laugh you will not lie you will learn by the number I will teach you now get up on your feet you had best unfuck your self or I will unscrew your head and shit down your neck