John Scalzi has posted An Incomplete Guide to Not Creeping, i.e. how not to be that guy women avoid at cons. He's got a number of good points -- but I wanted to follow up by giving two examples, of situations I've been in where it could have been creepy and wasn't.
See, sometimes you get guys responding to this kind of thing by wailing that they'll never be able to compliment a woman again, or whatever. And that just isn't the case. You can say nice things to a woman, or even touch her -- or even try to hit on her! -- without weirding her out. Here's how.
A year or two ago, teleidoplex and I were at a Shpongle/Infected Mushroom concert. The music was great, but also loud enough that she and I ended up hanging out in the upstairs lobby, sitting on a bench and chatting. (We could still hear the music just fine.) At one point during this, a guy came over and told us he really liked the skirts we were wearing.
He was totally not sketchy. In fact, he was really sweet and cute about it. In fairness, I will note that I got the impression he might be gay, which does indeed help the "I'm not here to skeeve on you" vibe. But there are a number of things he did right, that are totally within the reach of any human regardless of gender or sexual orientation.
1) When he approached us, he stopped outside of conversational range -- maybe half again or twice as far from me as teleidoplex was. This avoided boxing us in where we sat, and didn't make it seem like he was trying to join us uninvited.
2) I believe (though I may be misremembering) that he bent or crouched down, so that he wasn't looming, either. Given that we were sitting, this was also nice.
3) He complimented our clothing, not how we looked in it. Like, "I just wanted to say that your skirts are really cute" -- not "you look great in those skirts." Major non-skeeve points! (And this can apply even in situations that are less about "cute." Telling somebody her dress is gorgeous is waaaaaay different from telling her it makes her look hot.)
4) Having delivered his compliment, and us having thanked him, he said "have fun!" and bopped off back to his friends.
Result: teleidoplex and I were entirely delighted, and spent a moment marveling at how well he'd done that without ever once seeming sketchy.
But, I hear you say, that's just a passing compliment for your skirts. What if a guy is hoping to strike up an actual conversation? How does he do that without weirding you out?
Let's look at two hypothetical success modes for that, where "success" is defined as "being not creepy." Both start with the guy approaching as described, delivering his compliment, being thanked, and then saying, "What do you think of the concert?"
Hypothetical #1: I say, "It's fantastic! Kind of loud, though -- that's why were out here. But I've never heard either of these groups live before. How about you?"
I am, in this scenario, looking at the guy, responding to his question with information about myself, and asking him a question in return. This sends the signal that I am interested in talking to somebody new, not just my friend on the bench with me. Success! He can move closer (into normal conversational range), and so on from there.
Hypothetical #2: I say, "It's pretty cool."
In this scenario, I'm not really looking at the guy, and I probably glance at teleidoplex, advertising that I'd like to get back to the conversation I was having. I don't really engage with the guy, and I don't give him an open invitation to talk more. This is his cue to say "Cool, have fun!" and bop off back to his friends, with no harm done.
No, he hasn't gotten the conversation he was hoping for -- but pushing wouldn't get him what he wants, either. His path to success is to accept that and go look for some other woman to chat with. There are many girls, and many concerts, and the world will not end if I don't want to talk to him. Acting like it will . . . that is a fast train to creepiness.
Given that a lot of the creeper-vs-noncreeper discussion has revolved around geek conventions, and that backrubs are a thing that come up a lot at such events, let's talk about how to offer one of those without skeeving the recipient.
I often have tension in my shoulders, and have been known to need a backrub. I do not, however, accept them from just anybody. Mostly I accept them only from people (male or female) I already know pretty well, because it's an interaction with a high risk of creep factor. But I've gotten enough offers that I can tell you pretty clearly how to do it without weirding me out. (Other people's mileage, of course, may vary. What I say here is general advice, but if you really want to be safe, confine your offers to good personal friends only. Or don't give backrubs at all.)
1) Don't offer to a total stranger. If she doesn't know your name, or hasn't been talking to you for the last hour, she probably isn't going to accept. So why waste your time and risk creepiness by offering?
2) Wait for a sign that she wants a backrub. If she's stretching her neck, or rubbing her own shoulders, or saying "god, my back is killing me," then this is a sign that she might be glad for some assistance. Don't offer out of the blue to a woman who doesn't seem to need one.
3) Phrase it in a way that makes it clear it's totally up to her. "Would you like a backrub?" or "I could give you a backrub, if you like." NOT "Let me give you a backrub!" Grammatically speaking, the first two are conditional, and the condition is the woman saying "yes." The third one is a command. Which do you think is going to make her feel more comfortable?
4) Do not, repeat, DO NOT touch her while offering. Don't even hold your hands out. Keep your hands to yourself unless and until you're invited to use them.
5) If she accepts, then stick to safe zones -- basically, the non-neck bits of the trapezius. If you want to do anything more, ask. Don't feel up her neck, go into her lower back, move her arms around, or reach further forward than the tops of her shoulders without saying "do you mind if I . . ." I have accepted things like a guy putting his arm across my collarbone to brace me, but only when asked first, and when I've been sure he's really just trying to work the knots out.
6) There's tension in the "knotted muscle" sense, and there's tension in the "I'm not comfortable with this" sense. A woman who wants the massage you're giving her will do her best to relax into it. If her whole body is stiff, she's not okay, and you should ask if she'd prefer if you stop -- or just cut the massage short.
7) If she says "thanks, but I'm okay," then accept it and move on with the conversation. DON'T PUSH. Pushing signals "I think I know better than you what you need" and/or "I don't respect your boundaries" and/or "I'm really eager to get my hands on you." In other words: creepiness.
So: guys! You are allowed to say nice things, to indicate interest, to offer touch! The key is not to push. Give the woman her space (which includes not approaching her at all if the circumstances aren't right), pay attention to the signals she gives in return, and if you're rebuffed, don't take it personally. She doesn't owe you anything. Speaking for myself, I can't recall a single instance where I've been offended by a guy who accepted my lack of interest. The offensive ones are the ones who ignore those cues and keep trying.
But remember, too, that I am speaking for myself here. I do not speak for All Women, and there may well be comments on this post expressing different views. This is why the #1 key to not being a creeper is to actually get to know the woman in question -- to learn what she's interested in, where her boundaries are, and so on -- before you venture anything that might come across as forward. Until you know that, play it safe.