A word to Americans
To any Americans who feel they can't understand the humor because they're not Australian, just make a couple of substitutions. Instead of January 26th, think July 4th, and imagine a history teacher asking, "What is the significance of July 4th to Americans" and getting back, "We get to stay home and have a barbecue." Pretty much the same reaction. And then the dad would say "Next time, mention the fireworks". See, it crosses cultures, it's universal, and that's what makes it brilliant.