I can recall a few instances where upon hearing an assumption that I found to be offensive, I gave, in a blank tone, some piece of information that usually shot them up.
Racist acquaintance: Gypsies are worthless scum in our society, they all just sit around and steal or collect welfare.
Me: As a matter of fact, I can name at least five people that I happen to know and deeply respect who are Gypsies (enumerate: an NGO worker from whom I learned tons of valuable things, a sociology professor, a comedian, a psychologist, a journalist.)
Acquintance: What do you think you're gonna do with a diploma in philosophy? You'll end-up unemployed! Who will hire a philosopher?
Me: A lot of our graduates work in publicity, PR, cultural marketing, in ethics boards of corporations, in education etc.