At this point, using the term SJW in a discussion should equate to a Godwin, and mean that you lost the argument.
Pedantry aside1, Ferrari makes a good point. Increasingly, the accusation that someone is, or is behaving like, a “Social Justice Warrior” is bandied about online by reactionaries seeking to shut down discussions rather than deal with the points being made.
People who try to close down arguments in this way can, and should, be dismissed as the irrelevancies that they are.
1 Godwin’s Law merely states that “As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches 1.” The idea that making a Nazi comparison means that you lost the argument is a corollary.