What’s the difference?
Irony: a figure of speech in which you say (or write) the opposite of what you mean in such a manner that your listener (or reader) can tell what you actually mean.
This statement (last panel) is an example of irony.
Sarcasm: A subset of irony. Making an ironic statement in a way to intend some kind of rebuke.
The guy’s first statement in this comic is sarcasm:
And there you have it! Personally, I prefer irony to sarcasm. I think it’s my Minnesota background.