Sarcasm is easy once you understand the "rule". Basically, think of what you mean, find words that express the opposite, and speak them with a bit of edginess in your voice.
Sadly, knowing WHEN to be sarcastic is not so easy. And sarcasm at the wrong time is not good way to get along with people. Not that I have any personal experience with misplaced sarcasm.
Recognizing sarcasm is a problem too. Some people aren't very good at it and are obvious in their tone of voice and inflection. But someone that is good at it is much more subtle in their delivery. These sarcastic adepts trip me up all the time.
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When God made me He didn't use a mold. I'm FREEHAND baby!
The road to my hell is paved with your good intentions.