There's always somebody trying to conflate everyday sexism with courtship. What a pleasant surprise it's you this time, Larry 
FG2, fancying someone isn't wrong. Like all grown-ups, you're expected to know whether acting on that feeling is appropriate, and what actions would be acceptable.
We have courtship rituals (as an anthropologist might say!) and we all know what they are. Invasive behaviours like grabbing at someone, humiliating them, calling attention to their physical characteristics, demanding their attention and so on are hardly likely to win you a new friend are they?
Men don't do that stuff because they want you to like them, they do it because they feel entitled ... to make you feel bad. OK, that's rarely the explicit intention but what is? If a guy in a van shouts "Nice legs!" at me, what does he hope to achieve? Nothing, he'd say, it's just a laugh, it's a compliment if anything. But he doesn't know who the fuck I am; no-one appointed him the Simon Cowell of random women's legs, and I certainly didn't run up to his van yelling "How do my legs look in this?"
It's very unlikely he set out to piss me off but, equally, he's not doing it as a favour. To him it's not very different from admiring the scenery. Which means I'm scenery to him - but scenery he can shout at, in the assumption it will hear him. He doesn't care how the scenery feels about being yelled at; he just feels like yelling, so that's okay. And if I told him, helpfully, that his behaviour's offensive he would get a bit annoyed. He'd probably say I didn't appreciate being appreciated, men can't help looking at nice legs, etc, etc. In short, he would respond as you might expect a shouter to respond if the scenery told him to keep his opinions to himself. The scenery's opinion doesn't matter, does it? Scenery doesn't have views, it is the view! It should expect to be looked at and pleased if you show your appreciation. It's not like it's a person, is it ...