"Is your car stuck in the mud?"
"No, no, of course not. I'm only practicing how to spray mud using my tires.
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.
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?
Replier: What are you talking about?!? School sucks! You're retarded!
The word 'Sarcasm' is derived from a Greek word meaning 'tearing flesh', which is why sarcastic vegetarians are so ironic.
See also irony.
Dave: Oh, cool. That movie wasn't over-rated and shitty at all!
Bob: ...Sarcasm is the lowest form of wit, you know.
Dave: ...Fuck you.