I've told Carson since he was about 15, don't ever find yourself in a situation where you're not sure whether someone wants to have sex with you or not. And at the same time, as far-fetched as it may seem, don't let anyone pressure you to have sex if you don't want to.
But going back to when my kids were younger, I was guilty of the "Carson, give your uncle a hug." Or, "Allison, give your Aunt Tilly a kiss!" Yeah, it turns out that's not a great idea. I know that might seem a little over-reaching to assume that a hug from grandpa might mess your kid up, but I think the message is a good one: It's your body and it's your mind; you don't have to hug someone if you don't want to.
Back to the sex consent thing. Not only do we not want our daughters to have sex with someone they don't want to have sex with, we also don't want our young, usually clueless boys to think sex is something you should pressure someone into. Not to over complicate a basic human act, but it is a bit complicated. Did she have sex because you bought her three beers? Did she have sex because you wouldn't leave her apartment until she did? Or did she have sex because she wanted to? Cuz if it's not the last one, let's face it, it's not good for either party.
BTW, no one is paying me to plug parents.com but it's an awesome site that sends out a daily email with some great tips.