Before I start, I'm gonna say this: I'm gonna need some of you to take some supertaster tests. Cuz I'm half-certain some of you are supertasters.
Okay, so, best flavors, worst flavors. I'm a little bit of a food nerd, so 'best' is a hard call. It's probably somewhere between very fresh salmon grilled on a charcoal grill with little more than salt, pepper, and rosemary (oh god), the authentic, brick oven pizza in a tiny town in Italy when I was 21, or the orange blossom chiffon cake from a local dessert place (I wasn't expecting this cake to be ANYWHERE NEAR as good as it was. I'm usually a chocolate person, but this made my eyes roll back in my head.)
As far as non-food flavors, I have to second @VibrantFox about cotton. It's pleasantly benign.
Okay! And for really unpleasant flavors...
Green. Bell. Pepper. It is one of the hard nope things I won't eat. Reminds me of vomit. No one in my household will eat it, and neither will my parents. I would sooner eat limburger cheese a second time than voluntarily eat green bell pepper. (Limburger isn't as bad as it smells, but it's not good either.)
I'm not a fan of the lingering bitter aftertaste of antacids either.
As a bonus, though, my husband says that the worst thing he's ever tasted, hands down, no contest, was a prescription mouth wash for stopping major infections, or preventing them before oral surgery. He doesn't remember the name of the compound, only that he can still remember the flavor more than a decade later.
Edit: For your reading enjoyment, here's his actual review of the prescription mouthwash in question:
"As far as that mouthwash goes I can only describe it, as a super taster, as tasting like bad. Not tasting bad, which it does, but tasting like Bad, as if it were some nightmare taste that oozed forth from outside the cosmos and coalesced a form from the platonic ideal of something tasting terrible. Every taste bud I wish never detected anything going off at once in a sanity-rending epiphany on the nature of true oral torment.
If someone told me I had to use it three times a day for a week or I would literally die, I'm not sure I'd make it past Wed."