1. flaca means slim. 2. this is used in south america, mostly in argentina i think. 3. if you call a girl like this you intend something with her body and don't care about any other thing. 4. the use of k is funny, that's true (for some) and it is used in chatting, telephone messages, etc. but the main use among juveniles and not so juveniles of k nowadays in spain is as a sign that you support ideologies ranking into rebel causes: anarquism, antisystem, radical,, etc. also as K is an usual letter in basque language is also used in graffiti for people that are ready to support terrorist actions or what is called in basque "kaleborroka" = literally: street fighting (molotov bombs, destroying urban mobiliary, attacking political parties houses and the like. so if you ever come to this country, watching the graffitis in the walls you can have an idea of what kind of people you may find around.