I've had plenty of ropey glasses of water (chemicals, fluoride, iron) and off milk. But my all time champion is Greene King IPA, absolutely the most foul, disgusting beer I have drunk in 34 years of legal alcohol consumption. The one pint I managed to finish didn't taste remotely of beer, more like weak golden syrup with some unspeakable additives. Many years ago, I had a glass of Merlot which tasted like burning rubber. My guess is that it wasn't off but needed longer in the bottle to mature. Regardless, it was horrible.
My late parents were both fans of pastis drinks such as Pernod and Ouzo. Just the smell was enough to put me off. Eww.
Decades ago, I'm reliably informed that the ubiquitous Watney's Red Barrel was the gold standard for witchpiss in the brewing industry.