“A guy walks into a bar...” is a typical form of what has been called the “bar joke.” A math version was posted on Reddit—Jokes on February 28, 2018:

“The square root of -1 walks into a bar. The bartender looks on, amazed, and says ‘This is unreal.’”

Different versions of the math joke were posted earlier. “Ok, so the square root of -1 walks into a bar to talk to the hot blonde. She says ‘get real’” was posted on Twitter on January 14, 2014.


Reddit—Jokes
So the speed of light, e, and the square root of (-1) walk into a bar…
submitted December 27, 2012 by artymccluer
So the speed of light, e, and (-1)1/2 walk into a bar. The speed of light heads over to the bartender and gets his drink pretty quickly, as he’s wont to do. Then (-1)1/2 goes and orders his drink, and e just flips out on him. The square root of -1 asks e what’s wrong, and he says, “I came in here first, and you just went in front of me!” (-1)1/2 just says, “Hey, man, I’m just following the rules here!” Finally, the bartender gets fed up and says, “No, no, no, you idiot, it’s i before e except after c!

Twitter
Stephen Bell‏
@stevebwriter
Maths joke of the day: The speed of light, the square root of -1 & the natural logarithmic constant go into a bar… Punchline?
1:24 PM - 27 Dec 2012

Twitter
John Bauer‏
@theshrubbist
Ok, so the square root of -1 walks into a bar to talk to the hot blonde. She says “get real”. 
Ha ha. #AsianMathHumor
6:25 PM - 14 Jan 2014

Twitter
null‏
@Not_GarrettM
So pie and the square root of -1 walk into a bar. Pie says to the square root of -1 “get real.” So the square root of -1 says “be rational.”
5:48 PM - 6 Apr 2014

Reddit—Jokes
The square root of -1 walks into a bar.
submitted February 28, 2018 by SlipperySalmon2002
The bartender looks on, amazed, and says “This is unreal.”