Common newbie mistake there. Especially if you haven't had it before, you have to spread it on VERY VERY THIN. As in just a tiny amount.
I remember watching the Today Show when they did a broadcast of the Americas Cup in Western Australia in the late eighties, and Willard Scott decided to sample some Vegemite. I watched in complete horror as he spread it on a slice of bread like peanut butter. He must have put a whole tablespoon on there, if not more. The look on his face was priceless, poor guy! It's like a beautiful rare spice, you just use a little, it's not a bland filling like processed cheese that you scoop on. Sorry to labour the point, us Aussies are passionate about Vegemite! I am very impressed that some of you guys are going to give it a go :-D :-D