“A guy walks into a bar…” is a typical form of what has been called the “bar joke.” One popular science joke is:
 
“Helium walks into a bar. The bartender says, ‘We don’t serve noble gases in this bar.’ The helium doesn’t react.”
 
Brian Malow, self-proclaimed as “Earth’s Premier Science Comedian,” popularized the joke in a video from December 2008.
 
   
Wikipedia: Noble gas
The noble gases make a group of chemical elements with similar properties: under standard conditions, they are all odorless, colorless, monatomic gases with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).

For the first six periods of the periodic table, the noble gases are exactly the members of group 18 of the periodic table. It is possible that due to relativistic effects, the group 14 element flerovium exhibits some noble-gas-like properties, instead of the group 18 element ununoctium. Noble gases are typically highly unreactive except when under particular extreme conditions. The inertness of noble gases makes them very suitable in applications where reactions are not wanted. For example: argon is used in lightbulbs to prevent the hot tungsten filament from oxidizing; also, helium is breathed by deep-sea divers to prevent oxygen and nitrogen toxicity.
 
Twitter
Garth Webb
‏@garthwebb
Helium walks into a bar & the bartender says “we don’t serve noble gases here”. Helium doesn’t react.
7:43 PM - 1 Nov 2008
 
YouTube
Brian Malow: Science Laughs
Wonderfest Science
Uploaded on Dec 18, 2008
Brian Malow makes us laugh at Science Laughs, Bay Area Science Expo, Wonderfest 2008
http://sciencecomedian.com/
6:23
“Some helium gas drifts into a bar. The bartender says, ‘We don’t serve noble gases in this bar.’ The helium doesn’t react.”
 
Twitter
soundedfury
‏@soundedfury
Helium walks into a bar.  The bartender says “we don’t serve noble gases here.”  The helium doesn’t react.
6:17 PM - 11 Jan 2009
 
Twitter
◅ Rob Coyne ▻
‏@robcoyne
“A helium atom walks into a bar: the bartender says ‘we don’t serve noble gasses in this bar,’ the helium doesn’t react. But you should!”
12:50 PM - 21 Jul 2009
 
reddit
So Helium walks into a bar and orders a beer… (self.funny)
submitted August 29, 2010 by heck_yes to /r/funny
The bartender says, “Sorry, we don’t serve noble gases here.”
Helium doesn’t react.
 
Demotivational Posters
ARGON WALKS INTO A BAR - Bartender says “We don’t take kindly to Noble Gasses here.” Argon doesn’t react. demotivational poster
Zook #115268 Created August 31, 2010
 
NPR
Two Scientists Walk Into A Bar
APRIL 01, 2011 1:00 PM ET
IRA FLATOW, host:
This is SCIENCE FRIDAY. I’m Ira Flatow.
(...)
LICHTMAN: Wait, I have one, Ira, from our Facebook page that just came in. Michelle Tarik(ph) writes: A noble gas walks into a bar - it’s another bar joke. The bartender says: We can’t serve you here. The noble gas does not react.
 
Mr. MALOW: Yeah, you’ll find in that very same video clip.
 
LICHTMAN: That seems like (unintelligible)...
 
Mr. GOLDBLATT: They’re all Brian’s jokes.
 
Google Books
5,000 Great One Liners
By Grant Tucker
London: The Robson Press
2012
Pg. ?:
Some helium floats into a bar and tries to order a drink. The bartender says, ‘We don’t serve noble gases in here.’ The helium doesn’t react.
   
Business Insider (Australia)
Explanations To 13 Jokes Only Smart People Understand
JILLIAN D’ONFRO FEB 2 2015, 10:50 AM
(...)
When Helium walks into a bar and orders a beer, the bartender says, ‘Sorry, we don’t serve noble gases here.’ He doesn’t react.