We have an exclamation mark (!) to show a loudly-spoken sentence or one with exclamation or surprise. Usually these sentences [ended in !] are louder than usual sentences, to show surprise or that the speaker did not expect something, or they need to get something said quickly (as for why the human voice gets louder when the speaker is in danger/worried/scared, we must look back to the origins of mankind for that. Though I don't know exactly, it is probably something to do with hunting instincts or coming across predators).
So what if you want to express sarcasm? Well, that's where today's writers have to let you work out where sarcasm happens.
Yet suffer no more! I think there should be a sarcasm mark, or part of punctuation which shows sarcasm, instead of the funny way which is just using mock-HTML tags:
Hows about something like the exclamation or question mark?
Then I carried out my original idea, to have a curvy body to an exclamation mark, to show a lack of solid insult/statement, as if it were not completely 'meant'.
Which are also used in German, though in Danish you can also use:
Thank you and goodnight.
Oh and Jimmy McGee.