“HTML” usually stands for “Hypertext Markup Language,” the standard markup language for creating web pages. A backronym (back acronym) joke has been printed on many images:
   
“I know HTML (How To Meet Ladies).”
   
A photo of this T-shirt was posted on flickr on March 2, 2006.
 
     
Wikipedia: HTML
Hypertext Markup Language (HTML) is the standard markup language for creating web pages and web applications. With Cascading Style Sheets (CSS) and JavaScript it forms a triad of cornerstone technologies for the World Wide Web. Web browsers receive HTML documents from a web server or from local storage and render them into multimedia web pages. HTML describes the structure of a web page semantically and originally included cues for the appearance of the document.
     
flickr
kris krüg
Taken on March 2, 2006
I Know HTML
Jer’s new shirt.
 
Twitter
Thejesh GN‏
@thej
I know HTML ( how to meet ladies)
9:45 AM - 1 Oct 2007
   
Google Groups: comp.lang.php
how to produce a tooltip ( like one we have in VB ) ?
John Dunlop
11/18/07
(...)
XHTML (How To Meet Ladies, X-Rated) is, ahem, different.
 
Interesting and Beautiful Pictures
Funny T-shirts
December 31st, 2008
funny text on t-shirts.
(T-shirt shown.—ed.)
html-how to meet ladies
 
6 June 2013, The Clarion-Ledger (Jackson, MS), “Nerd Culture Explored: MPB: Geek the new cool?” by LaReeca Rucker, pg. 3B, col. 1:
Do a quick search on Google, and you’ll pull up a variety of geekery, including T-shirts with sayings like:
(...)
* I know HTML (How To Meet Ladies)
   
Google Books
Icarus
By Deon Meyer
New York, NY: Grove Atlantic
2015
Pg. ?:
It showed Ernst Richter in jeans and a blue T-shirt with H.T.M.L. on it, and below that (expert in) How To Meet Ladies.
 
Fast Company
06.08.15 MY CREATIVE LIFE
How To Meet Ladies: Decoding “Silicon Valley” Player Erlich Bachman’s Zen-Bro Look
Aviato’s founder is more than the sum of his amazing T-shirt collection. Here, Silicon Valley‘s costume designer unpacks his style.
BY EVIE NAGY
(...)
Then there are Erlich’s T-shirts, emblazoned with nerd humor like the element “Nintendium,” the message “I Know HTML (How To Meet Ladies),” and the binary code for bitcoin.
 
Twitter
gross ass baby hands‏
@gross_hands
Worried that I’ll make a “How To Meet Ladies” joke in a job interview when asked about my HTML experience
8:49 AM - 6 Sep 2017