Christopher Warner : What is verbal irony?

Christopher Warner at TED-Ed  (transcript)
What is verbal irony?
Summary
The meaning of the words seems to change depending on the circumstances. It turns those words into not only irony but also sarcasm. It’s blurry because it’s not good if people understand clearly.
Thus the words sometimes show the true, though, it sometimes shows the opposite of what you mean seems to be irony, and verbal irony seems to include sarcasm sometimes.

How about the following?
“You really work hard!”
1, Compliments and it’s true.
2, If you are told when you don’t work is irony because it’s the opposite.
3, If you are told when you don’t have better results, you work, though. It’s probably sarcastic!

Thus it must be difficult to be used and understand, mustn't it? OMG!
You will lose weight! You are beautiful!

Words in this story
sarcasm /noun/ the use of irony to mock or convey contempt.
sarcastic /adj/ marked by or given to using irony in order to mock or convey contempt.
raging / tense, violent, fierce,
blurry /adj/ weak, hazy