B'gosh and begorrah! Oy vey! WTF?!
Sarcasm is a tricky thing in print. No sly grins, quick winks, gentle horse collar hugs or gentle elbow pokes in the ribs as encountered IRL. Familiarity breeds understanding.
Italics won't hack it. When a responding poster "cites" a previous post, all is italic and the distinction is lost in "translation." Anything in bold is interpreted as being stressed and important.
Emoticons are an option but I've yet to see a tongue-in-cheek smiley thingy. Comic Sans might work but it needs to be an easier option. "J/K" and "I keed, I keed" work but strike me as far more work than should be necessary.
As for me – ****-em if they can't catch or take a joke. I clearly offer no definitive solution. My apologies.