I thought "cunt" and "pussy" both mean the same in English, except when they are used to describe a person: "cunt" is arrogant, pushy and narcissist and "pussy" a coward. "Vittumainen" as an adjective describing a person does mean the former (as a general adjective it can mean irritating, difficult and/or generally unpleasant), but there is no idiomatic or direct translation for the latter meaning because there are no cowardly Finns. However, when referring to female genitalia, "cunt" would be translated as "vittu" and "pussy", as a less harsh, perhaps "pillu" (still meaning the birthing canal), though "vittu" would not be exactly wrong either.
Idiomatically, "vittu" is also indeed equivalent to "fuck", because there is no comparable Finnish word (all direct translations used to describe only the act of copulation). Then there is the word "vitutus", which roughly means "feeling very irritated".