Taking to the UK. Joke, as requested:
A horse walks into a bar, and orders a drink. The bartender says "Say, horse, you're in here rather often - do you think you might be an alcoholic?".
The horse says "I don't think I am.", and promptly disappears.
You might notice that this is a reference to Descartes' "I think therefore I am" statement. I could have pointed that out before I told the joke, to make it funnier, but that would have been putting Descartes before the horse.