"fetid" is great descriptor. It to me feels more visceral than "rancid".
I think I disagree with "grape" being the worst though. Artificial grape flavor is the most honest one, be it medicine or soda. It's the distant cousin that shows up to the wedding or funeral in a t-shirt, shorts, and flip flops; it's the octagenerian emeritus faculty member that shows up to seminar and sits in the front row and sleeps through the presentation; it's the Kazaa (or Morpheus or Limewire) file labeled "Blink182.mp3.exe"—you look at it and you know exactly what you're gonna get.
Japanese and Mexican for the sake of the question. It's what I grew up eating, and I hate the idea of being without my familiar comfort foods.
Truthfully though, I love eating too much to limit myself regionally or to just two countries. There's so much I haven't tried.