“A guy walks into a bar…”  is a typical form of what has been called the “bar joke.” A superconductor version is:
 
“Yttrium barium copper oxide (YBCO) walks into a bar. The bartender tells him, ‘We don’t serve superconductors here.’ He leaves without resistance.”
 
The joke was posted on Reddit—Jokes on January 19, 2017.
 
“A room-temperature superconductor walks into a bar…” is the original form of the YBCO joke.
 
   
Wikipedia: Yttrium barium copper oxide
Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds, famous for displaying “high-temperature superconductivity”. It includes the first material ever discovered to become superconducting above the boiling point of liquid nitrogen (77 K) at about 90 K. Many YBCO compounds have the general formula YBa2Cu3O7-x (also known as Y123), although materials with other Y:Ba:Cu ratios exist, such as YBa2Cu4Oy (Y124) or Y2Ba4Cu7Oy (Y247).
 
Reddit—Jokes
Yttrium-barium-copper oxide walks into a bar
submitted January 19, 2017 by procastonator
The bartender tells him, “We don’t serve superconductors here.”
He leaves without resistance.
 
Twitter
Dan The Funny Man
‏@FunnyFirehose
Yttrium-barium-copper oxide walks into a bar http://bit.ly/2jR7sNh  #jokes
2:01 PM - 19 Jan 2017
 
Twitter
Lame Jokes
‏@lamejokes_net
Yttrium-barium-copper oxide walks into a bar http://ift.tt/2iXYGP5
The bartender tells him, “We don’t serve superconductors here.”He le…
2:02 PM - 19 Jan 2017
 
Twitter
lol
‏@idiot_detected
Yttrium-barium-copper oxide walks into a bar The bartender tells him, “We don’t serve superconductors here.“He leaves without resistance. #…
5:45 PM - 19 Jan 2017