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

“f(x) walks into a bar and asks for a drink. The bartender says, ‘Sorry, we don’t cater for functions.’”

The joke has been cited in print since at least 2004.


Google Groups: alt.ozdebate
Got any nails?
Typhoid
9/24/04
f(x)=6x+3 walks into a bar. “Got any sandwiches? f(x)=6x+3 asks the barman.

“Sorry,” he replies, “We don’t cater for functions.”

Google Groups: uk.rec.humour
Yet another bar joke…
Hyphen
6/22/05
f(x) went into a bar and asked for a drink.

The bartender said “We don’t cater for functions”...

Webdeveloper.com
PhP Joke
nshiell
09-28-2005, 06:59 AM
So

function test(v1, v2)
{
global $hello;
$hello = “1”;
echo $hello + $hello;
}

walks into a bar and asks for a pint of beer and the bar tender says “sorry we don’t cater for functions”

Hoops (Australia)
Matt Ryan
23:21 31 Oct 05
“f(x) = 3x+2” walks into a city pub and says “Listen, I’m turning 21 and I would like to hold my birthday party here.”

The owner says “I’m sorry, but we don’t cater for functions!”

LiveJournal
Monument (marnanel) wrote,
2006-11-05 21:33:00
Fireworks Night
(...)
f(x)=3x² walks into a bar and asks for a sandwich. “Sorry,” says the barman, “we don’t cater for functions.”

the observers hunch
TUESDAY, MAY 08, 2007
Poor Physics Jokes
(...)
z=x^2+3xy Walks into a pub, sits down on the barstool and orders a pint.
The barman looks up from the glass he’s polishing and says “Sorry mate, you’re gonna have to leave. We don’t cater for functions”.

Twitter
Becky Haycox
‏@hambox
sin(x) walks into a bar and asks for a drink. Bartender says, “Sorry, we don’t cater for functions.”
12:32 PM - 28 Jul 2008

Straight Dope Message Board
Geeky Jokes
VunderBob
11-19-2008, 07:59 AM
Two spiral galaxies go into a pub. “Get out” says the landlord; “you’re barred”.

f(x) goes into a pub. The landlord says “Sorry, we don’t cater for functions”.

f’(x) goes into a pub. The landlord says “Sorry, we don’t cater for functions”. (This may look like the same joke, but it’s not; it’s derivative humour.)
This one took me a minute, until I realized my typeface and astigmatism obscured the apostrophe.

f ‘(x) goes into a pub… “.

Twitter
Jemima Kiss
‏@jemimakiss
f(x)=2x+3 walks into a bar.  The barman says, “Sorry, we don’t cater for functions.” (@liquidindian )
8:48 AM - 17 Dec 2008

Google Books
Extremely Embarrassing Dad Jokes:
Because Dads Don’t Know When to Stop
By Ian Allen
New York, NY: Pavilion Books
2015
Pg. ?:
F(x) walks into a bar and asks for a sandwich. The landlord says, ‘I’m sorry, we don’t cater for functions.’

Google Books
Algebra for Applications:
Cryptography, Secret Sharing, Error-Correcting, Fingerprinting, Compression
By Arkadii Slinko
New York, NY: Springer
2015
Pg. 132:
A polynomial walks into a bar and asks for a drink. The barman declines: “We don’t cater for functions.”
An old math joke.