Jackie Chan (Wong Fei-Hung) nearly lost an eye when Jang Lee Hwang (Jim Ti-Sam) kicked him in the head during the final fight scene. When Hwang became aware of this, he refused to do more takes for the shot.
The drunken boxing style exists in real-life, originating in China. In Chinese, it is called "Zui Quan" (sometimes called "Zuijuquan"). But unlike in the movie, it is dangerous to perform the art while drunk because serious injuries can occur.
There is a clip (possibly a teaser or a deleted scene) in which Wong Fei-Hung (Jackie Chan) demonstrates drunken boxing on the front lawn of Beggar So's home. The latter calls instructions throughout, with characters subsequently appearing on-screen. It appeared in the documentary "Cinema of Vengeance" and later as a "deleted scene" on some home video releases. A photograph from this (Fei-Hung with his leg raised, holding both a tea cup and wine jar) is commonly used in various artworks.