Second most disgusting drink I've ever run into: Bacon Soda.
This took some doing.
Truly.
In Summer of 1989, as part of the tour of Germany I was with, we spent an afternoon in East Berlin. At lunch, being a soda freak kid, I asked for a cola, and was presented with something called "Margo Kola". This was the Eastern-block Coke-cola substitute. It has a foam head that put most beers I'd seen to shame. I sipped, and it was fine. As soon as I took the glass away from my lips, the aftertaste hit. Pure, 100% saccharine. Dis-GUSTING. Was it really that bad? I tried again. Oh, Flying Spaghetti Monster, yes. Yes it was that bad. Am I dumb enough to try again. Yep. Oooh. Quick, give me some kerosine to wash out the taste.
A friend didn't believe me. After the Fall of the Wall, he managed to get hold of some. He agreed. Most disgusting drink. Ever. Worst that fermented camel urine.
That record stood for over 20 years. I suspect that after the Fall of the Wall, and collapse of the Eastern Block, Margo was discontinued for health reasons.
Last year, one of my gaming group (who is in to the whole weird sodas thing) bough 3 "Bacon-flavored Soda" bottles. The smell alone churned my gut, and I declined to poison my tongue. Everyone else in the group was un-thrilled.
Last month, there was a "Buffalo Chicken Wing" soda. No one even wanted to try it. Based on odor and past experience, I list that as 3rd most disgusting beverage.
#1 most disgusting beverage: Bacon-flavored Soda
#2 most disgusting beverage: Margo Kola
#3 most disgusting beverage: Buffalo Chicken Wing-flavored Soda