I think vittu is the worst. It used to be just a normal anatomy word like... I don't know, hundred or some decades ago, but now it's a really rude swearword. Some teenagers use it instead of um or a comma or a pause in their sentences or when talking. Like every other word is vittu. But there's a place for that too, especially if something really, really, really bugs you.

My favourite swearword is perkele. Sometimes helvetinperkele. Those mean the devil and the devil of hell. (Are there any other kind?) :D Saatana (the devil, again) is good too but not so powerful as perkele. :D You see I have a very close relationship with devil.