Back in the early days of my current relationship, before we were officially together, my SO punched me in the dick. We were at the Renaissance Festival, drinking a bit, and she grabbed something from my hand and ran off with it. I took off after her, caught up, and grabbed at her shoulder. On instinct she spun right around, fist swinging in low, and socked me right in the junk. I collapsed to my knees. About a minute later the nearest security guy came by and said "That was the funniest damn thing I've seen this month, but you really need to clear the path for others." That was the point I realized this girl was awesome, and this relationship could be going places.
I try hard to respect people. Part of respecting people is not hitting on them inappropriately. Unfortunately there are few clear rules on this matter. Be friendly, flirt, read cues, back off if the other party isn't interested. Don't hit on people at work (yours or theirs). Feel free to hit on people at bars and parties. But things in real life are fuzzy. For example - how do conventions fit in to this? Some people think of them more as work, others as more of a party. Not too long ago an open couple propositioned someone in a very ham-handed way, as recounted in this blog post. They approached a speaker at a con, whom they'd had some cursory contact with previously, and handed her a card with a topless photo as an invitation. They probably felt they were being honest and non-threatening, but the speaker was mortified and felt sexually harassed.
I'm especially wary of this as I call myself a feminist, and making women feel less safe is antithetical to what I'm working towards. I'm also very sex-positive; and so I only want to approach women/couples who are open to such an approach, and remain platonic friends and colleagues with those who aren't. It can be difficult to determine who is receptive and who isn't, as there's no way to ask without implying your intent (yes, I know about Down (formerly Bang With Friends), but haven't used it). Due to social custom it generally befalls the man to initiate these interactions, so even when you're fairly confident the feeling is mutual, the guy is the one who has to take the risk of looking like a creep and making the women feel unsafe. It's possible to misjudge a person or situation, maybe falling for wishful thinking. There is an omnipresent danger of crossing lines you didn't mean to cross.
What's worse - sometimes you won't even know you're doing it. Social pressures are so fucked up that - flying in the face of all reason - women are strongly discouraged from letting men know when they're being creepers or assholes! The term "strongly discouraged" is a massive understatement. Take ElevatorGate. Rebecca Watson (who is fucking awesome!) was at a con, drinking into the wee hours. She went to retire to her hotel room, and a guy who'd been lurking around followed her into the elevator, and when they were alone and trapped together propositioned her. She said that this was uncomfortable/creepy, and mentioned in a video "Guys, don't do that." This was GREAT advice, given with a smile. It is good knowledge to have, and is particularly useful for young geeky males who don't have a lot of experience with women and need to know these sorts of things. It should have gotten nods from the experienced and thanks from the inexperienced. Instead Rebecca was subjected to a months-long intimidation and harassment campaign, including daily rape threats and death threats. The words "ElevatorGate" still live in infamy. Because a woman dared to make the world a slightly better place for everyone who isn't an enormous asshole.
I try to err on the side of caution, but there's always some doubt. My now-SO had already demonstrated assertiveness/self-possession/honesty. But we'd only known each other a couple months and I was still wary. The dick-punch was like an exclamation point. It drove home that yes - she really was willing to assert her agency in all aspects. I would never have to worry that I was doing something to irritate or hurt her which she wasn't letting me know about. I could trust her to look after her own interests, I could let go of always second-guessing my actions. She was an equal, not a thing to be protected.
It was the best start I can imagine for a relationship. :)