A couple of thoughts here (as a man who has been around):
1. Its true that a [straight] man will imagine what its like to have sexual relations with a female co-worker if she is halfway decent looking and/or nice. For the most part, this is just an involuntary, fleeting though—not something you ponder or act on. It tends not to happen with women who are relatively unattractive, old, or have bad personalities.
2. I seriously doubt that mature men imagine female co-workers have a “secret crush” on them. The exception is if women give real signals to this effect. These signals can range from obvious flirting to less subtle things, like laughing at your banter (even when its not really funny), hanging around for longer than they have to, lingering eye contact, unnecessarily close physical proximity or even offering to pay for things. This last one is a subtle, but surprisingly good indicator—perhaps because woman may not think of it as a signal. Even if you have fleeting sexual thoughts about a woman, most men can tell if ia woman is truely interested or not.
3. The most disingenuous statement in the world is when a woman says to a man: “But....I thought we were just friends.” All women over 18 understand male-female dynamics very well. Women realize how men are wired and can intuitively tell when a man is attracted to them. And they use it for all its worth—especially when a) they are not attracted to us and b) they know we won’t act on it. At the end of the day, when it comes to using sexuality, they are the professionals and we are the amatuers.
Brother, you are giving women *waaaaay* too much credit. I didn't figure it out until I was 26. I was happily married and working in a male-dominated job. One by one, all but two of the guys I worked with made a pass at me at one point or another.
I was truly shocked and horrified. I honestly did not see it coming. My husband had warned me and I didn't believe him.
The way female friends interact with each other (hugging, doing nice things for one another, intense personal conversations) was natural for me. When I started making friends with the guys, I treated them the way I would a good female friend. I NEVER thought that these idiots would see it as flirting. (Alright - *I* was the idiot.) They knew I was happily married. I thought that my ring was all the clarity that I needed.
My daughter is 20 and just now starting to figure it out. (Her dad and I have beat her over the head with this reality since she was 14... 'he wants to have sex with you'...)
No. Young women are pretty oblivious. And that can go on for much longer than it should because she doesn't *want* it to be true. Who wants to lose a good friend? So even when the reality starts to set it, she'll push it away for as long as she can because friendship means so much to her.
I think a woman offering to pay for things is most often an intentional indicator of not being romantically interested—and so not becoming indebted or open to accusations of leading a man on.