DEAR MISS MANNERS: What is an appropriate and polite response to a compliment that I know is disingenuous? And upon receiving such a compliment, am I required to return one that is equally disingenuous? I ask because someone I know invariably compliments me on something I’m wearing, my hair, etc. I’m not a stylish person and my hair tends to be a mess. Her compliments have the consequence of making me feel self-conscious, looked-over and, ultimately, lied to. GENTLE READER: The safe answer is, of course, “Thank you,” which Miss Manners points out can be delivered in a way that subtly undercuts…