Define The Oldest Trick In The Book Meaning

The Oldest Trick In The Book
A trick most people know about, if you try to trick someone and they say ¨thats The oldest trick in the book, then it means they know what you are trying to do and, to quote Robbie Rotten, ¨Try something else¨.
Remember just because someone knows what you are trying to pull, does not mean they are untrickable.
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Guy1: Hey, look over there!
Guy2: Bruh, that's The oldest trick in the book.
By Marni