Toast. Until it's almost burnt.
Butter.
Solid thin layer of vegemite to cover every possible millimeter. Similar to this
Note: I have many, many years of building up vegemite resistance. Newcomers to vegemite should never attempt this. Beginners start with at most something like this instead. Lots of people like even less than that. Start with less; you can always add a little bit more on.
Also, very occasionally, if I don't feel hungry but feel like I should have something, a vegemite sandwich hits the spot. The softer the bread, the better. I don't put as much vegemite on as on my toast. So, it's almost a butter sandwich with a slight vegemite flavour.
The last way I'll have vegemite is on crackers. The crackers must have holes in them, and you must put one on top of the other so that you can squeeze it to make the delicious butter & vegemite worms pop out. Which you instantly lick off. Vita Weats used to do the job well. Recommend butter on both crackers, but vegemite only on the bottom cracker, otherwise you have too much vegemite!
Fun fact: Since 2017, Vegemite is now owned by the Bega group, not Kraft. Bega Group is a public company and close to half of the shares are still held by Bega's farmer-suppliers, while the rest are owned by public investors