Responses

Yup it's derivation from 'kara' and I went to double-check to avoid misinforming you guys and I found it in master's thesis from our most prestigious university regarding all synonyms for genitalia as karina is a bit old term and people dont use it that often.
Full name of thesis is "gender sterotype in jargon of croatian language" in sociologic study so science confirmed. I am from Croatia but this jargon can be used in Bosnian and serbian language also (in central eastern Europe, south slavic languages)
Crap, my mum's name is Karina...Not exactly the association I'd like to have during the snu snu scene.