here's why Gyaru is a tag and why's Osanajimi and Tomboy is not implemented as a tag(yet).
Most manga have that kind of Osanajimi things goin' on with their manga, it's not essential, since it's not a telling something (character behaviour), its only tells you that the character is this guy's childhood friend's. Meanwhile Gyaru is essential, because its telling you the character type, she's a gal (duh) using so many make up and bling bling on their ears or something gal. https://en.m.wikipedia.org/wiki/Gyaru just read it. too lazy to explain.
You said, but Tomboy is a character (to tell a behaviour of some females that's too males).... well, yes i agree with you, but there's an exception, this kind of things is just.....
you know what, i agree with tomboy theme. here's some 1+ for tomboy
actually i'm secretly disagree since im too lazy to explain it.