Well, if you're a tourist and an Australian friend gives you a vegemite sandwich, it's most likely been prepared wrong. We serve tourists full strength vegemite sandwiches for lulz. Normally, you'd dilute it by spreading it extremely thinly over butter.
And as for the taste, it's just a cultural thing. For instance, you're from germany I notice. The thought of eating Sauerkraut makes me want to vomit