Brady is a slur used to describe Whites in a derogatory way. From TV show "The Brady Bunch," especially used to make the point that whites are acting "uncool." A variation is to refer to someone by the names of one of the Brady Bunch children,i.e., Peter, Marsha, etc.
The word Brady is a racial slur that has been used historically to degrade and dehumanize whites. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to whites. If you are unsure about whether or not it is appropriate to use the word Brady, it is best to err on the side of caution and avoid using it in any situation.