Fish would drown and birds will fall.
My informant describes this saying as a holler to girls when they are at parties or walking down the street. Whenever a pretty girl would walk by, one of his friends would shout out to the girl, cham yu law ahm, which would sometimes be a compliment or could be as rash behavior.
Because the Chinese are often modest, this action would not be acceptable to partake in the presence of adults.
The saying goes back to an ancient Chinese saying regarding a very beautiful girl. She was so beautiful that it was said that the birds would fall from the sky and the fish would drown in the water.
It seems nonsensical and completely impossible that both of these occur that similar times, therefore emphasizing the beauty of this woman. She is so beautiful that everything in the world turns backwards and natural turns reverse.
If smooth enough, a suave young Chinese boy could use this saying as beautiful poetry and woe his respective love. Unfortunately, my informant has not succeeded in using this.