I said it earlier in jest, but the correct answer is still 'good music'.
This answer mocks the fundamental vanity and narcissism of the attempt by the questioner to boost their own ego by asking in the first place, the subjective nature of taste (anything you like is automatically 'good' after all) and, by making such an outrageous statement, implicitly acknowledges that you are not making any claim to authority and that no set of preferences is objectively better than any other.
Of course, they might just think you're an arrogant twat - it all depends on the delivery.