That is not a literal translation though, just the closest English equivalent.

"Devil's cuntheads" would be a close-to-literal translation (I'm Finnish)

...Although "perkele" is a native god, and it can be debated whether it should be translated to "devil"; http://en.wikipedia.org/wiki/Perkele

"Perkeleen" is used nearly synonymously with "fucking" though (as in, "devil" isn't really considered swearing in the English language). I read it as "fucking cunthead". Which is lovely indeed!

Disclaimer: my knowledge of the Finnish language is mostly limited to profanity.

I'd rate 'perkeleen' to be slightly 'softer' than 'fucking'. 'Vittu' (or 'vitun') is the best translation for 'fucking'. Not sure if there's a better word for it in English, but maybe something like 'damn' or 'bloody'.

Reading Finnish out loud (with a somewhat German-y pronunciation) always manages to cheer me up.

So you've understood the Finnish national mood - the exact opposite to how you felt after swearing :)