What is "be there or be square"

phr. (context US British humorous English) (non-gloss definition: Used to encourage someone to go somewhere.)

Be There or Be Square is a 1998 Chinese romantic comedy film directed by Feng Xiaogang, produced by Beijing Forbidden City Film Co. Ltd., Beijing Film Studio, Zhongji Modern Commercial, Beijing Zhengtian Media & Culture Centre, and Sleiman/Tyrol Films. It is a Feng Xiaogang hesui pian ("New Year celebratory film"), screened during the 1999 Chinese New Year to boost box office takings, and it earned 30M Yuan in theaters. It was granted "Best Feature Film - Hua Biao Prize in 1998" to Beijing Forbidden City Film Co. Ltd., Beijing Film Studio, Zhongji Modern Commercial, Beijing Zhengtian Media & Culture Centre by the China State Administration of Broadcast, Film, & TV in May 1999.

Ge You and Xu Fan star as Beijing natives working in Los Angeles, whose paths constantly cross in a foreign city. They attempt to balance work with friendship/love in spite of mounting disasters each time they meet.