As you saw in the last lesson, sarcasm falls into verbal irony. It's when a person says one thing, but means another. At first it may seem like praise or something good, but really it is an insult or means something negative.
"I LOVE when my plans get canceled." It's sarcastic because, in general, people don't like when this happens.
"This is my amazing new TV, that doesn't work." It's sarcastic because it comes off as praise, but really it is an insult. Poor TV...
And... our last example: