The fact that I am prohibited by my government from setting off fireworks to celebrate liberty, independence, and freedom, on a day my government says is an important official holiday for celebrating liberty, independence, and freedom, but I am only allowed to celebrate liberty, independence, and freedom in a manner approved by my government, is an example of “Tyrannical Irony”
Both you and the OP have a really good grasp of the meaning of “sarcasm”, don’t you? (That is sarcasm.)
In fact, you are both wrong, and have things backwards.
I think this confusion arises because people often learn the concept of sarcasm before they learn that of irony, and thus are misled into thinking that sarcasm is the simpler, more inclusive concept. However, the reverse is the case. Sarcasm is irony that is intended to be hurtful. The example given by the OP does not seem to be intended to be hurtful. It is irony but not sarcasm.
It is not a fact that is relevant in this case, however. The problem is that both the OP and Ms Morissette (who is Canadian, anyway) do not understand the concept of irony, and use the word incorrectly. The meanings of “irony” and “sarcasm” do not differ between US and UK English, and I am sure there are people who confuse the two on both sides of the Atlantic.
“Sardonic”?
I am not sure what your point is. Unlike sarcasm, I do not think being sardonic has to involve irony (although it may).