Warren W. answered 03/28/19
I am an ESL instructor who enjoys helping students make more money.
Okay, so, first thing, your teacher wasn't wrong. It sounds better in a formal situation to use the article. That is why your teacher informed you that you 'must' use it. They wanted you to sound correct and educated.
However, remember that with English there are typically exceptions to rules unlike other languages.
What you are referring to is related to slang or street language. Typically, in slang, words are shortened or not even used at all. For example, "Y'all" comes from "You all", drop the 'ou'.
So, it sounds like the movies you are watching are likely have scenes with characters in less-than-formal conditions.
Hope this helps. ~W
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