Seven Eight

It is pronounced as "qiba" in Chinese, and it sounds similar to "jiba" in Chinese, which means penis, and Chinese people often use penis as a swear world, so every time they want to swear but without using the real bad word, they will use "qiba", which is seven eight to instead.

Rude way: You are so jiba stupid
Polite way: You are so qiba(seven eight) stupid