Most browsers, IM clients and email applications do not have sarcastica installed thereby leading to ambiguity and confusion in text based conversations.
Sarcastica was invented to prevent these situations by the Minister of Practicality in 2010 and has yet to find mainstream adoption. Despite it's practicality and usefulness universal adoption was deemed to be 'a whole thing'.
Frodo: Heading off to Mordor to destroy the One Ring of Power and save the world from the Dark Lord's wrath. Wanna come?
Sam: WTF? You serious?
Frodo: nah, kidding. My sarcastica font isn't working again.