I always thought the reason that boys weren't supposed to wear pink in a couple of countries was because those countries had begun to associate pink and blue as being gender-specific, and that boys were not to wear pink because it was not a ¨boy color¨, and some parents are afraid of their children identifying in any way with the other gender. I have heard parents make the argument that they want their child's gender to be evident in public, so there are no mistakes made in addressing them. Not because it is confused with a smaller physical stature or less physical strength.
I don't really see how your other examples play outside of these strict gender lines, and into weakness, at all. The fish that I have had to net are the ones that fight so badly that I cannot get them into the boat. You don't have to net a quiet fish. They just sit on the line and do what you want. It's the fighters that require netting. I have never equated femininity with weakness. Are you sure this is a common perception in the West?
I state again that I only speak for myself, and since I'm an idiot, it's probably wise to discard my ramblings
... With that said:
While, like you said, parents usually don't want their children identifying with the opposite sex, I think that weakness is considered very disadvantageous for a boy. Not just physical weakness, but mental weakness -"Don't cry like a baby", or even better, when they say "Don't cry like a girl".
Roughness in girls is likewise considered disadvantageous. Tattoos and muscles are much less acceptable on females in society than on men.
You could argue that society simply does not like people to cross gender lines, blur the boundaries of their sex, and take on traits associated with the opposite sex, but since being male is almost always associated with being strong, it's difficult for women to take on any strong traits without being seen as masculine and no longer feminine.
Tattoos, muscles, wearing camo, an interest in violent things, etc. would all be considered masculinizing for a woman -because they are associated with strength. An interest in science is associated with men but would not be considered masculinizing on a woman because it's not associated with strength.
A certain amount of strength is acceptable for women in the context of sex
. For example, a woman brandishing guns and wearing hunting gear is still feminine if she is doing it in a sexy manner, but otherwise it's unfeminine (ie. too strong).
And yes, I do think that Britney Spears great success hinged on her image of "weakness" as the vulnerable, virginal teen sweetheart (Hit me baby once more time? I'm a slave 4 U?). I think many people are sexually attracted to weakness.
Gentlemen have always worn pink.
Yes, "Gentle"men have always worn pink, the emphasis on the "gentle" part. They are wearing pink to put emphasis on a softer side. Men can have a soft side, as long as it isn't too soft, because then they're acting "like women".
Just my dumb thoughts. I probably don't make much sense since I didn't sleep last night! I have a habit of rambling... it's only gotten worse since I learnt to touch type so now my fingers can keep up with my rambling brain. Well, I'll shut up now...