The "-holic" suffix means the person has an addiction or constantly does that thing. It's derived from "alcoholic", ie. always drinking alcohol. A sarcasm-holic is someone who constantly uses sarcasm. But then, I still wonder if they are being sarcastic by introducing themselves as a sarcasm-holic.

When you add "-holic" to something it means you are addicted to it, some examples: alcoholic-addicted to alcohol chocoholic-addicted to chocolate (people joke and say they are chocoholics if they eat a lot of chocolate) So when the person said he was a sarcasm-holic it means he is really sarcastic. I've never heard anyone say that before though.