As far as I know, we are the only country in the world that swears with illness and disease. We actually swear with anything we can come up with.
They say it's the rudest form of swearing in the world. Swearing in English is extremely harmless compared to the stuff we're throwing out here. For some people it's actually a hobby to make as many (original) combinations of horrible things as they can in one sentence. You can be really creative. In addition to that, some sounds in the Dutch language are very harsh, and often used in these words to underline the rudeness with aggressive sounding vowels. For example, we make a very harsh kind of 'G' that is pretty unique. It pretty much sounds like you're trying to clear your throat as obnoxiously as possible.
Only Arabs can come close to making that same sound.
I'd give examples but it would probably be very shocking to most of you, and I'm not looking for a ban.
I have this friend from Manchester... he was in tears from laughter as I was trying to translate the swearing I was doing into English. He found it so hilarious that he was thinking about actually trying to say those things to people back home in England. But he said it would be so beyond rude that people probably just wouldn't know what to say or think.