Juniper can be a killer for me, but I've learned that oftentimes a listed note can be spun in so many ways or played with such subtlety that my opinion of the scent can be the opposite of what I expected. A good example is Onda EdP in that the idea of passion fruit in fragrance is totally unappealing to me, but it works so well in this one. With that said, rose is generally my kryptonite, as well as anything connected to desserts.
EDIT: Yep, I have to add aquatics and chemical "clean" scents. I forgot to mention them here because it's a whole genre that I've managed to block entirely. Anything along the flankery lines of Issey Miyake, Allure, and stuff like that is just an instant no go in my book. Nauseating to the point that teal-colored bottles now scare me.