An exaggeration is when someone says "That guy was a big as a house" or "His brains the size of a peanut".
A wit is kind of like a smart remark that makes fun of someone in order to change then just like with John Wilkes when he was told by a constituent that he would rather vote for the devil, Wilkes responded: "Naturally." He then added: "And if your friend decides against standing, can I count on your vote?".
An oxymoron is when something said or done contradicts itself like "jumbo shrimp" or "new classic".
Sarcasm is when someone says something but means either the opposite or something different like when someone tries to make a joke and you reply, "that's hilarious!"