To elaborate, one argument against cultural relativism is that the idea itself is another form of ethnocentrism. Because apparently, cultural relativism puts itself in a higher moral ground than ethnocentrism.
So for example, consider this argument by Timothy Keller, who writes in his "The Reason for God":
Many say that it is ethnocentric to claim that our religion is superior to others. Yet isn't that very statement ethnocentric? Most non-Western cultures have no problem saying that their culture and religion is best. The idea that it is wrong to do so is deeply rooted in Western traditions of self-criticism and individualism.
So if I were to follow this reasoning I find this statement to be also problematic.
Don't judge me.
Because I am implying that it is bad to judge, therefore I have judged him.
But I don't think relativists would have problems with those kind of statements. And frankly, I find the entire argument against relativism above to be quite absurd, but I kinda don't know as to why.