How safe is it to combine flavor extracts?
I probably would not recommend eating a box of baking soda and chasing that with shots of vinegar. But aside from that silliness, I can't think of a single thing that is actual "food" that is unsafe mixed with another actual "food", assuming reasonable quantities. Certainly anything with alcohol can be dangerous in huge quantities, as can a lot of other ingredients. Allergies or food sensitivities can make certain ingredients dangerous to certain people. But mixing ingredients to which the individual has no special sensitivity and in normal quantities? No, I don't think you are risking anything by doing so other than unpleasant food.