The script that writes the joke builds pseudorandom sentences out of pseudorandom words, using a very basic branching series of Markov chains. The words are built from hiragana in ways that "sound" verb-y or adjective-y (etc) as required. Sometimes real words are formed, more often than not they are gibberish. A small built-in glossary consolidates some "close-enough" words. The joke always starts with "A bad customer walks into a bar", and ends with "Thanks for your custom!"
Bad Customer is probably funnier in pseudo-Japanese, but for non-speakers (at the request of Soanyway), Google Translate provides a further layer of semantic dissociation.
Bad Customer. Click here for a new iteration of the joke.