“A guy walks into a bar...” is a typical form of what has been called the “bar joke.” A prism version is:

*“A rectangular prism walks into a bar and the bartender asks, ‘Why the long face?’”*

The pun is on the famous “Why the long face?” punchline of the “A horse walks into a bar...” joke. “A rectangular prism walks into a bar and the bartender asks ‘Why the long face?’” was posted on Twitter on May 6, 2013.

Wikipedia: Prism

In optics, a *prism* is a transparent optical element with flat, polished surfaces that refract light. At least two of the flat surfaces must have an angle between them. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use “prism” usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, plastic, and fluorite.

Twitter

paste

@ericsmellsfunny

A rectangular prism walks into a bar and the bartender asks “Why the long face?”

1:50 PM - 6 May 2013

Reddit—3amjokes

So a rectangular prism walks into a bar self.3amjokes

Submitted November 30, 2017 by MikeOShay

And the bartender asks, “Why the four long faces?”

Twitter

LOL Tweets™

@lolmgco

So a rectangular prism walks into a bar

And the bartender asks, “Why the four long faces?”

2:17 PM - 30 Nov 2017

Twitter

3AM

@3AM_Jokes

So a rectangular prism walks into a bar… And the bartender asks, “Why the four long faces?”

2:40 PM - 30 Nov 2017

New York City • Restaurants/Bars/Coffeehouses/Food Stores • Wednesday, November 29, 2017 • Permalink