This statement comes from Dolphus Raymond, but it can apply to other characters in the story.
Dolphus Raymond is a white man who comes from an old, reputable family. However, he acts in a way that is the opposite from what most people would expect from such a person. He spends his time with black people, is constantly drunk, and has several children with a black woman.
People are shocked at this behaviour. However, we later find out that he does not actually drink in public. He simply pretends to do so. In this quote, he explains that his "fake drinking" is a way to give people an excuse for his behaviour. People can then explain his life by saying that it is the fault of alcohol, and that this is why he cannot be what they want him to be.
The phrase can apply to any character in the novel that needs to compromise his public image in order to be seen as someone who fits Southern stereotypes. An example of this is Calpurnia, as she changes her way of speaking depending on whether she is surrounded by white or black people.
