Actually, you can get pretty good Italian food in BKK, among other things. Thailand is the rice basket of Asia (lol) and there is lots of good stuff to eat everywhere. Ketchup on pizza isn't my thing, nor have I seen anyone do that, but it wouldn't surprise me at all. In the Philippines everyone douses their pizza in hot sauce, and if you get one to go, it comes with packets of hot sauce for your dining convenience!
Fish sauce is very necessary in most Thai cuisine, but I'm sure you can find something to eat with a little legwork. I eat and drink pretty much anything and will often go out of my way to try new food and drink. Thai cuisine is vast and regionally diverse, so I have a lot more exploring to do!
OK, it's definitely time for breakfast now.