“What do the Washington Metro system and the Little Mermaid have in common?” (joke)

The Washington (DC) Metro—a transportation system comparable to New York City’s subway—runs “under D.C.” In the popular Disney animated film The Little Mermaid (1989), the character of Sebastian, the crab, sings the Academy Award-winning song, “Under the Sea.” A joke is:
 
Q: What do the Washington Metro system and the Little Mermaid have in common?
A: They’e both under D.C.
 
“Now I’m singing a jingle for the Washington metro called ‘Under D.C.’ to the tune of the Little Mermaid song. What is up with you, brain?” was posted on Twitter on May 21, 2009. “What do Sebastian the crab and the Washington metro have in common? They’re both under D.C.” was posted on Twitter on June 15, 2015.
 
The joke was posted on Reddit on August 12, 2016.
 
   
Wikipedia: Washington Metro
The Washington Metro, commonly called Metro and branded Metrorail, is the rapid transit system serving the Washington, D.C. metropolitan area in the United States. It is administered by the Washington Metropolitan Area Transit Authority (WMATA), which also operates Metrobus service under the Metro name. Besides the District, Metro serves several jurisdictions in Maryland and Virginia. In Maryland, Metro provides service to Montgomery and Prince George’s counties; in Virginia, to Arlington and Fairfax counties and the independent city of Alexandria.
 
Wikipedia: The Little Mermaid (1989 film)
The Little Mermaid is a 1989 American animated musical fantasy film produced by Walt Disney Feature Animation and released by Walt Disney Pictures.
(...)
In January 1990, The Little Mermaid earned three Academy Award nominations, making it the first Disney animated film to earn an Academy Award nomination since The Rescuers in 1977. The film won two of the awards, for Best Song (“Under the Sea”) and Best Score.
 
Twitter
Laurie Voss
‏@seldo
Now I’m singing a jingle for the Washington metro called “Under D.C.” to the tune of the Little Mermaid song. What is up with you, brain?
10:44 AM - 21 May 2009
   
Twitter
Mike Sheldon
‏@mikesheldon
What do Sebastian the crab and the Washington metro have in common? They’re both under D.C.
8:00 AM - 15 Jun 2015
 
Twitter
Mike Sheldon
‏@mikesheldon
@mattl Rename the Washington Metro to ‘Sebastian The Crab’, because it’s under DC.
5:12 AM - 15 Sep 2015
 
Twitter
Elainovision Union
‏@scattermoon
Under DC. Under DC. Washington Metro runs by electro under DC.
5:34 AM - 28 Dec 2015
 
reddit
What do the Washington Metro system and the Little Mermaid have in common?
submitted August 12, 2016 by aljobar
They’re both under DC.