You might think this advice for men, but it's actually for everyone.
It's true that guys are often the culprits. For example: as I'm writing this I'm sitting in a pub with a female friend. A bloke just came over to us to asked for a light for his ciggie. We declined (neither of us smoke). Five minutes later, he's back at our table again wanting to know 'where the good clubs are' (it's five on a Wednesday afternoon.) He's clearly looking to strike up a friendship with one or both of us (probably my friend, because she smiled at him when we sat down.) But we have our notebooks and laptops out, and it should be obvious that we're working and not looking for dates.
He's not a bad guy. He's just 'having a go' at hitting on some chicks in a bar, perhaps with less social awareness than average. But despite our polite refusal to talk, he keeps coming back with new questions. We don't want to say 'go away' because we can see he doesn't mean any harm. Also, he's had a few drinks and we're afraid that telling him to go away might make him angry. So we just sit here, try not to make eye contact and hope he gets the hint.
Experiences like this are the reason it's so difficult to talk to women in public. We're always trying to avoid risky situations. It means that even when we do want to meet people, we'll often shut down conversation from strangers because we're nervous.
It's not just guys that are the problem. It's a fact that most of us suck at flirting - I've been sexually inappropriate, insensitive and have missed the signals that my object of affection wasn't interested. I have also been the victim of sexual harassment by other women. Because Aussie gendered culture assumes women are never the sexual aggressors, some ladies don't have a very good awareness of the times they invade the personal space of others. (Try going to a women-only strip show e.g. a hen's night, and you'll see exactly what I mean.)
When I was twenty years old I hung out at a lesbian bar in Sydney with my friends. The older ladies all had punk haircuts and acted tough. I thought they were cool. But one time, a woman took a liking to me and got all up in my face about it. She said "you're a keeper!" and then she literally picked me up and started carrying me away from the pub, down the street. I mean, what the fuck? I was saying "put me down" but she laughed it off. To be clear, this was someone I had never met before and we hadn't agreed to any physical contact. I didn't know where she was taking me. Finally I convinced her to put me down and I got back to my friends. I don't think she really wanted to abduct me.. She was simply demonstrating to me that she was bigger, stronger and tougher than me, and because she found me attractive, she could do whatever she wanted.
Here are a couple of ways to ensure your attention is wanted.