I’m from burgerland, what the hell is vegemite?
Without getting into the ingredients, Vegemite is essentially a very salty spread you put on toast. The reason a lot of non-Australians balk at it (speaking as someone who doesn't like it) tends to be that they just heap some onto a spoon and eat it, rather than spreading a thin layer onto some toast. It's a bit like heaping a spoonful of butter, which would be much less appetising than just spreading it onto toast. Seeing as it seems to be uniquely Australian I don't blame people for not knowing how to eat it.
It's also... not really as big a thing here the international perception of Australia suggests? Like it exists, and people eat it, but personally at least it's not really a part of my every day life. My family doesn't really eat it, I've never had breakfast with someone who was eating it, when cafes have toast options the spreads are usually butter or jam, etc. This could also just be because it's so normal that very few people just casually bring it up in conversation.
Like "g'day mate", people use it, it's Australian, but it's not a MASSIVE thing. And for the record, while I have heard people call a barbecue a "barbie", what USamericans call "shrimp", we call "prawns".