Do I win a prize or something, 'cause after many years of answering that question ("Does this dress make me look fat?") indirectly or just avoiding the question, I finally told my wife "No, it's your rear end that makes you look fat, the dress merely accentuates it. <short pause>. What do you actually expect me to say?"We have a winner!
BTW for those boys out there who have yet to face this question: RUN!
There is no good answer. If you say "No honey, you look great!" she thinks you don't care about the fact that she thinks she's getting fat, and if you avoid the question it'll be taken as a "yes" and will usually get you a trip to sleeping on the couch. For the record, my wife laughed about it and hasn't asked me that question that way since.
BTW, it really all depends on what the OP is after. IMHO, being a jerk is no way to have a meaningful relationship with anyone, but having the confidence and insouciance of a jerk will generally get you more attention from women just from the fact that you will have more chances to ask a girl out than the stereotypical "nice guy".
Even if only 1% of women will ultimately say yes, the jerk who just asks 100 women out every month will come out ahead over the nice guy who spends a year preparing to ask one woman on a date in just the right way.
B