The sentence is criticizing professors who say that there is no universal morality: nothing is inherently good or bad, it depends on the culture. It says that if you damage such a person's car, they will get mad at you, and act as if you did something morally wrong, even though their philosophy says that nothing is morally right or wrong. In other words, the sentence is saying they are hypocrites who only hold this view (relativism) when it doesn't affect them personally.