If you are already in a relationship, you probably have figured this one out by now. Women are delicate creatures in more ways than one, meaning that if you think you can just "tell us like it is", you have another thing coming, buddy. Even if you've got one of those low-maintenance type of gals who you like to think of as "one of the guys", it's quite likely that she still has a pretty fragile ego.
Unless you are a complete and total moron, you would never go around pointing out her flaws directly, but it doesn't take you pulling out a magnifying glass to feel like we're being judged. We know we have flaws--even the most confident-seeming woman is probably much more insecure than the average man. Take the amount of flaws you have noticed in us and multiply them times at least 5, and that's probably the amount we've tallied up ourselves. It isn't necessary to point these things out to us, is what I'm saying. We've got it covered. There's a lot that goes on behind the scenes that you don't ever see, and much of that is concentrated on hiding our flaws from you in the hopes that you never notice them.
Unfortunately, it doesn't take you saying, "Hey, your ass is getting really big--better lay off the ice cream," to bruise a woman's ego. We can take a seemingly innocent comment from you and turn it into a dig on us, especially if we are having a bad day.
For example, say you and your lady-friend are watching tv together when a Pro-activ commercial comes on. And say you've noticed that her skin has been less-than perfect lately. The first thing that comes to your mind is to suggest ordering the magical skin-clearing system, but any idiot knows that's the wrong way to go. So instead, you say something along the lines of, "Wow! That Jessica Simpson sure has some great skin now--what a difference!" You may not know it, but you just made her want to put a bag over her head. Not Jessica Simpson, dumb-ass--your woman.
Believe it or not, even though you didn't say anything about her directly, she was thinking along the same lines as you were. She was holding her breath, hoping you weren't noticing her bad skin while looking at the pore-less woman on the screen. The moment you opened your mouth to talk about acne, she felt every single blemish and pore on her face magnify to the size of Mount St. Helens, which in turn made her feel self-conscious. Sad, but true.
So how do you put this knowledge to good use? Clearly it's not practical to censor yourself with every breath, so here's a pretty easy rule of thumb to follow: don't talk about any thing pertaining to any one of her flaws. This list includes, but is not limited to: acne, fat, cellulite, varicose veins, body/facial hair (on women only), and saggy/too-small boobs. The list is different for every woman, so adjust your banned-topic list to your female companion. Don't go overboard and start complimenting her on her perceived flaws ("Your skin has looked really good lately!") because we see right through that. When in doubt, just keep your mouth shut and give her a hug or a kiss--works every time.