“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” A version about the names of the days of the week is:
       
“4 Norse gods, 1 Roman god, and 2 astrological bodies walk into a bar. The bartender says, ‘Oh, this is gonna be a week joke.’”
   
The joke was posted on Reddit—Jokes (using “astronomical bodies”)  on January 8, 2020, and on Reddit—Dadjokes (using “Astrological bodies”) on October 29, 2020. 
     
       
Reddit—Jokes   
Posted by u/physicsphantasm January 8, 2020
4 Norse god, 1 Roman god, and 2 astronomical bodies walk into a bar
The bartender says ” Oh, this is a gonna be a week joke”
 
Twitter
Lar
@Lar_Swagener
4 Norse gods, 1 roman god, and 2 astronomical bodies walk into a bar.
The bartender says, “Oh, this is going to be a week joke.”
6:00 PM · Jan 8, 2020·Twitter for Android
     
Twitter
Anthony Poirier
@AnthonyPoirier1
Four Norse gods, one Roman god, and two astronomical bodies walk into a bar.
The bartender says, “oh, this is gonna be a week joke.”
11:55 PM · Jan 8, 2020·Facebook
   
Twitter
Matt W-S
@Yakcall
4 Norse god, 1 Roman god, and 2 astronomical bodies walk into a bar
The bartender says ” Oh, this is a gonna be a week joke”
5:42 PM · Jan 9, 2020·TweetDeck
 
Twitter
Gender Binary Ghost (Halloween Name)
@RiverInsanity
4 Norse Gods, 1 Roman God, and 2 Astrological bodies walk into a bar.
What does the bartender say?
5:12 PM · Oct 1, 2020·Twitter for Android
 
Twitter
Mark Strong
@PhoManCho
Replying to @stefnoble
4 Norse Gods, 1 Roman God, and 2 Astrological bodies walk into a bar.
The bartender says: “Oh, this is gonna be a week joke.”
8:30 AM · Oct 28, 2020 from Syracuse, NY·Twitter for iPhone
 
Reddit—Dadjokes
Posted by u/Outi94 October 29, 2020
4 Norse gods, 1 roman God, and 2 astrological bodies walk into a bar
The bartender says: Oh, this is gonna be a week joke
 
Twitter
The Law Offices of Hall & Copetas
@HallandCopetas
A Roman god, four Norse gods and two astrological bodies walk into a bar together.  The bartender rolls his eyes and say “Oh, this is gonna be a week joke.”
Don’t hate us because we’re beautiful with the #dadjokes.
8:55 AM · Oct 30, 2020·Twitter Web App