Not things that are dangerous or inedible to eat the day-after.
Rather, things you simply don't find palatable as leftovers -- something you refuse to eat on a purely, subjective level.
For me, I simply cannot stand leftover fried rice. Dunno why, probably because fried rice is already sort of like a leftover dish since it's usually, and best, made with day-old rice.
Reheated leftover fried rice inevitably tends to be grainier, less fluffy, with a more pronounced oily aftertaste. Just not very good.
And cold fried rice is just a nonstarter.
What's on your refuse-to-eat-as-leftover list?