Fellas, this one's for you. You know the old adage, "Honesty is the best policy?" Well I'm here to tell you that this adage needs to be revised as follows: Honesty is the best policy, most of the time. Without further ado, here are the six specific situations when honesty is not the best policy (oh, and Jill's comments are in red):
(1) When your significant other asks you if your ex-girlfriend was attractive.
The answer should always be, "she was average or maybe slightly above-average, but not nearly as attractive as you."

(2) When your significant other asks you if you think she's gained weight recently.
The answer is always, "no." Always.
Jill says: I had to break this down for Jack--we women always, ALWAYS know when we've gained weight. So if you think you're being helpful by pointing it out, well, you're not. It's called "kicking us when we're down and then not getting any lovin' for a while because now you've made us feel like we're gigantic and disgusting looking!" I don't recommend it.
(3) When your significant other asks you if she's the best lover you've ever had.
The answer is always, "yes." Always.
Jill says: What self respecting human asks this anyway? I mean, if it's not offered up, chances are you're not #1....so by asking, you're either going to hear a truth you don't want to hear and then obsess about it, or you're going to hear a lie and know it's a lie. If he doesn't tell, don't ask.
(4) When your significant other asks you if you find her best friend attractive. I don't care if her best friend is Angelina Jolie; you do not think she's attractive! If you can't bring yourself to lie, say something ambiguous like, "I think she's nice."
(5) When your significant other says something like, "My mom can be a bit annoying sometimes, can't she?"
This is a trap. Do not agree with her. Trust me on this one, please.
(6) When your significant other shows you a picture of Wendy Larson - her arch-nemesis in high school - and asks you if you would have had any interest in dating her when you were 17.
Ideally, you should wince and say, "Uggh, no way."
Jill says: That Wendy Larson was a whore! I don't care what you say, she was a dirty little trollop whose breast size was inversely proportionate to her brain size (note: BIG boobs, tiny brain, in case I lost any of you there with my math-like talk).
So if you ever find yourself in any of these six situations, please remember: honesty is not always the best policy. Let me know if you think I missed any.