According to the connoisseurs at ratebeer.com, Old English 800 is the worst beer in the world. Here's one review:

Bad aftertaste, rancid mouth. Not fit for students, bums or the desperate for a drink. Nothing but horrible taste and booze. I am less of a person for having consumed this.

At the link, you can see a list of the fifty worst beers as determined by these reviewers.

What's the worst commercially available beer that you've tasted?

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