As it happens, rude words are one of my specialist subjects in Finnish! I'm not proud if it, but it is.
Rude words are often the first words one learns in a foreign language. Indeed, in the early days of my Finnish learning career, such words probably accounted for over 50% of my vocabulary!And yet, in any language, if a foreigner uses rude words or slang, it's at best comical and more often just wrong. So why is it that we end up learning such words if we can't use them?
Firstly, I would postulate that swear words are easily identifiable in a conversation because they are emphasised and often repeated. For example I learned the Finnish swearing trinity of "vittu, saatana, perkele" on football pitches in Helsinki. At first, I thought those words meant something like "oh dear, I somehow failed to score despite being in front of the empty goal" or "I say old chap, that tackle was rather vigorous". Of course it was soon clear those words were in fact RUDE. The v-word (one of the rudest and most common Finnish swear words) refers to the female genitalia and is used pretty much in the same way as the f-word in English. The slightly less offensive s- and p-words both refer to the devil. Thus predictably, the VSP combination expresses a real irritation or frustration. Hence the football connection.
The second reason why foreigners learn rude words quickly is because the natives find it funny to teach them those words. I remember quite clearly having a nice lunch at a terrace in Helsinki on a warm summer's day with some (male) colleagues when the subject of whether to have eggs in our salads came up. I already knew the word for egg (muna), but one of my colleagues could not resist teaching me that it also referred to the male genitalia. Cue Finnish sniggers about whether I wanted muna in my salaatti. Hohoho!
On an other occasion, I was having dinner with colleagues in Vienna of all places, when the bottled water I had ordered was placed in front of me. The water was "Acqua Panna" from Italy. The Finns around me could began to snigger. It turns out "panna" means not only "to put, to insert, to stick", but also an action of a sexual nature. Cue: "Dying for panna?" Hohoho!
But remember: we already know quite few rude words in Finnish and swearing is neither big nor clever!