Jokes about the September 11, 2001 terrorist attacks on New York City’s World Trade Center are numerous, although not politically correct. One such politically incorrect joke is:
   
Q: Why are the twin towers and genders so similar?
A: Because there used to be two of them, but it’s offensive to joke about that now.
   
The joke was posted on Reddit on July 2, 2016 and has been frequently reposted.
 
   
Wikipedia: World Trade Center (1973-2001)
The World Trade Center was a large complex of seven buildings in Lower Manhattan, New York City, United States. It featured landmark twin towers, which opened on April 4, 1973, and were destroyed in the September 11 attacks, with 7 World Trade Center collapsing later that day due to the damage it suffered when the twin towers collapsed that morning. The other buildings in the complex were severely damaged by the collapse of the twin towers, and their ruins were eventually demolished.
 
At the time of their completion, the “Twin Towers” — the original 1 World Trade Center, at 1,368 feet (417 m); and 2 World Trade Center, at 1,362 feet (415 m) — were the tallest buildings in the world
         
Twitter
Jokes & Gags
‏@Jokescomedyx
Why are the twin towers and genders so similar?: Because there used to be two of them, but it’s offensive to ... http://sh.st/Ggb3y
11:22 PM - 1 Jul 2016 (It appears that this, dated July 1st, actually follows the entry below, dated July 2nd.—ed.)
 
Reddit
Why are the twin towers and genders so similar?
submitted July 2, 2016 by DedotatedSkrub
Because there used to be two of them, but it’s offensive to joke about that now.
 
Reddit
What do the twin towers and genders have in common?
submitted August 30, 2016 by 7relos
There used to be two and now it’s too offensive to talk about.
 
Twitter
n9
‏@brojobs
genders are like the twin towers there used to be two but now if u talk about it youll probably offend someone
11:20 PM - 30 Aug 2016
 
Twitter
JĄMƏ§ ŔÂĪŅĔŞ
‏@RequadJ
Gender is like the Twin Towers. There used to be two, but now everyone gets offended when you talk about them.
9:11 AM - 10 Sep 2016
 
Reddit
What do the twin towers and gender have in common?
submitted September 19, 2016 by Dangerous_Pie_
There used to be two of them, but it’s offensive to joke about that now.
 
Reddit
How are genders like the twin towers?
submitted September 23, 2016 by Viking_RnP
There used to be two of them but now everyone gets offended if you talk about it.