The coolest thing about different languages —hell, even dialects— has to be swearing.
As a Dutchman, I can swear up and down, and you may just mistake me for listing the most notorious diseases known to our history. It’s how we live, sickness fills our curses and swears. Do this in English, and you’ll just get the strangest looks. “Just get cholera, y’all.” That doesn’t quite have the same ring “krijg toch allemaal de klere” does.
The same goes for dialects, though they mostly just bring forth additions to a language’s pile of swears. Little remarks that will have anyone from outside the area second-guess what they just heard, trying to figure out the intended meaning. Luckily, intonation frequently saves the day.
And then there’s the people who don’t speak their native tongues unless they’re really mad. You just know there’s some juicy foreign curses in there, but asking for translations would just add injury to insult.
Throw your most obscure curse at me, I dare you. (Hexes not allowed.)