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

“Oxygen, Hydrogen, Sulfur, Sodium, and Phosphorus walk into a bar. The bartender says, ‘OH SNaP.’”

The joke was posted on Twitter on April 26, 2010.

“Oxygen and Magnesium walk into a bar…” is a similar joke.


Twitter
silversilx‏
@silversilx
Q: What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorous walked into his bar?
A: OH SNaP!
10:25 AM - 26 Apr 2010

Twitter
Inorganic Ventures‏
@ivLabs
Q: What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorous walked into his bar?
A: OH SNaP! #fb
8:24 AM - 1 Sep 2010

Reddit—Chemistry
Oxygen, Hydrogen, Sulfur, Sodium and Phosphorous all walk into the bar. The bartender looks at them and says, ‘OH SNaP! (instantrimshot.com)
submitted February 16, 2011 by [deleted]

Yahoo! Answers (August 12, 2011)
Can somebody explain this joke to me?
What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorus walked in to his bar?
OH SNaP!

Best Answer:  The abbreviations for the elements. O being Oxygen, H being hydrogen , S being Sulfur, Na being Sodium, and P being Phosphorus

YouTube
OH SNaP!
dashedit
Published on Oct 25, 2012
Q: What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorous walked into his bar?
A: OH SNaP! - created at http://goanimate.com/

Reddit—Jokes
So Oxygen, Hydrogen, Sulfur, Sodium, and phosphorus walk into a bar.
submitted July 13, 2016 by BangedYourMum
The bartender says “OH SNAP”

Twitter
Thomas Scientific‏
@ThomasSci
Q: What did the bartender say when oxygen, hydrogen, sulfur, sodium, and phosphorous walked into his bar?  A: OH SNaP! #sciencehumor
7:40 AM - 15 Jul 2016

Reddit—Jokes
Oxygen, Hydrogen, Sulfur, Sodium, and Phosphorus walk into a bar.
submitted August 6, 2017 by wackoclown
The bartender says: “OH SNaP”