I would suggest writing original material rather than translation.Try to think Lojbanically, and just use whatever words you know,rather than worrying "what is the Lojban word for (X)." Don't try tosay anything fancy at first!
Lojban expresses most of what is expressed in English through sentence toneusing cmavo, particularly the UI cmavo. Translating UI cmavo intoEnglish words almost always sounds bizarre-- they're usually moreproperly translated by tone! For instance "zo'o" means "I'm sayingthis humorously," which is pretty silly to say in words in English,but we promise you that "zo'o" is a common word around these parts &it really does serve the same purpose as a "humorous tone" does inEnglish.
One sarcastic device that translates perfectly well into Lojban fromEnglish is English's "...NOT!" as in:I go to the market... NOT!.i mi klama le zarci ... naku sai!
But you've already said how to be sarcastic. When someone sayssomething you disagree with, take that statement to its logicalconclusion in absurdity, using a condescending tone. They have a modelof you in their minds, that you are not a dumb person who wouldbelieve an obvious absurdity. They recognize the logical absurdity andperhaps the tone of voice, causing them to suddenly bridge a gap intheir mind between your words and you real mental state. From acertain perspective, that phenomenon is not really linguistic, it'sentirely social, based on the models we make of each other's state ofmind. It makes no difference which language you're speaking. You cando it exactly the same in Lojban or English.