The phrase “be there or be square” means that someone should either attend an event or not be considered cool or fashionable. It is often used as a playful invitation or reminder to attend an event.
The exact origin of the phrase is unclear, but it is thought to have originated in the United States in the 1950s or 1960s. It may have originated as a play on the phrase “be there or be nowhere,” which was used to mean the same thing.
Here is an example of the phrase being used in dialogue:
Person 1: Hey, are you coming to the party tonight?
Person 2: I don’t know, I might have other plans.
Person 1: Oh come on, it’s going to be so much fun! Be there or be square!
In this example, Person 1 is inviting Person 2 to the party and is using the phrase “be there or be square” as a playful way of urging them to attend.