Bai Renzai probably means little fool.

It also depends on whether the tone is kind. Usually this is not what you really want to curse.

The word "Zi" can also mean "Xiao Zi" in Chaoshan dialect.

In Chaoshan dialect, the word "zi" can also mean a low meaning, which is similar to looking down on him. Adding the word "zi" only means that you really want to swear.