Be There or Be Square humorous
Used humorously to encourage someone to attend a certain event, and if they don't attend they will be considered boring.
Come on, there will be a lot of fun at the party! Be there or be square!
A: Will you come to my birthday party? B: I don't know for sure. I'll give you a call later. A: Okay! Be there or be square!
Children or adults often say this phrase to get their friends to join in something, especially to jump into a swimming pool (pond, lake, etc.)
Act with more effort or enthusiasm
To try to achieve something or succeed in honour of somebody
To motivate someone to do something better, more quickly or more passionately
This phrase dated from around the 1950s. It appears to derive from the slang word square which means "a person who is boring and out of touch with current trends."
Furthermore, the word square was used to describe someone who didn't appreciate jazz music around the time jazz became popular in the 1940s.
To do something in an unusual way
I guess I like to run against the grain in everything I do.