Well kiddo, sardonicism is when someone makes a joke or says something sarcastic, but they're not actually happy or amused. It's kind of like when a grown-up says "Oh great, just what I needed" when something bad happens, but you know they're not really happy about it.
So imagine you're playing a game and you're losing by a lot. Your friend might say, "Wow, looks like you're really killing it!" with a sarcastic tone. They're not really cheering you on, they're actually making fun of you for doing badly. That's sardonicism.
It's important to understand that sarcasm and sardonicism can sometimes be hurtful or disrespectful, so it's always best to use them carefully and with people who understand your sense of humor.