Idiot: I beat up a ten year old today.
You: That's impressive! (with a hint of sarcasm)
Idiot: I know, right!

Ex. 1: "I'm okay. Don't mind the gaping wound and the sword protruding from my back. I'm fine. Feel like a million fucking bucks, dammit."

Ex. 2:
"Is your car stuck in the mud?"
"No, no, of course not. I'm only practicing how to spray mud using my tires.

Jackass."

Mom: how was school today, son?
Son: it was fuckin' great, mom.

You walk into a hospital room where your friend is on a bed with his left leg, no arms, and only half of his prick. You say,"How ya doin, man?"
He says,"Oh, just great. I feel better than ever. I could just hop all around the world, I feel so great."
You say,"Really? That's some great news."

See, this isn't your friend trying to make you look stupid, which if you said one or both of these things, you might be, it was his immune system acting due to the high levels of stupidity being taken into his brain. It automatically responded with sarcasm. So don't take it personaly.

Rebecca Black is the greatest artist of all time! #FunFunFun

The statement above is obviously filled with sarcasm.

Twilight was a good movie, said a sarcasm-speaking Bolivian tree frog.

A random is painting his fence, when his neighbor comes up to him and asks a stupid question:

Neighbor: Oh, you're painting your fence today?
Random: No, I'm milking cows on jupiter, while drinking light soda and driving.
Neighbour: Was that sarcasm?
Random: Now, why would you think that?