“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” A lightbulb version is:
 
“A giant light bulb walks into a bar. The bartender looks up and says, ‘Hey! What’s the big idea?’”
 
The bar joke was posted on Reddit—Dad Jokes on April 5, 2017.
 
   
TV Tropes
Idea Bulb
A character thinks and thinks… then, suddenly, has a bright idea! A light bulb turns itself on directly above the character’s head. Often with character pointing one index fingers upwards. Sometimes accompanied by an Idea Ding.
 
This trope has been subverted for decades — it became a cliche almost as soon as it was invented (in the 1920s, for the black and white Felix the Cat cartoons).
   
Reddit—Dad Jokes
A giant lightbulb walks into a bar… (self.dadjokes)
submitted April 5, 2017 by hellslave
Bartender looks up at says, “Hey! What’s the big idea?”
 
Twitter
Tetet‏
@__Tetet_
A giant lightbulb walks into a bar…
Bartender looks up at says, “Hey! What’s the big idea?”
#dadjoke
4:34 AM - 6 Apr 2017
 
Twitter
Jillian‏
@SillyJillyStein
A giant lightbulb walks into a bar…
Bartender looks up at says, “Hey! What’s the big idea?”
6:38 AM - 6 Apr 2017
 
The Amazingly Lame Joke of the Day
Friday, April 7, 2017
A giant light bulb walks into a bar.
The bartender looks up and says, “Hey! What’s the big idea?”
Posted by Tim Wycislak at 1:45 PM