The 2019–20 coronavirus pandemic caused people to quarantine in their homes. Jehovah’s Witnesses who normally knocked on doors (or rang the doorbells) no longer did that.
     
“If you get a mail with as subject ‘ding, dong‘ , don’t open it it’s from a Jehovah’s witness working from home..” was posted on Twitter by DOGS & PEOPLE on March 22, 2020. “If you receive an email with the title ‘DING DONG‘, do not open it!!! It’s the Jehovah’s witnesses, working from home” was posted on Reddit—Jokes on March 23, 2020.
     
“Ding dong” is sometimes replaced with “knock knock,” making it a knock-knock joke. “If you receive an email with the subject ‘Knock Knock’... Don’t open it, it’s just Jehovah’s Witnesses working from home!” was posted on Reddit—Jokes on March 23, 2020. “If you get an email titled Knock Knock, don’t open it. It’s from the Jehovah Witness’s working from home” was posted on Twitter by Stay Home on March 24, 2020.
   
   
Wikipedia: 2019-20 coronavirus outbreak
The 2019–20 coronavirus pandemic is an ongoing global pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The outbreak was first identified in Wuhan, Hubei, China, in December 2019, and was recognised as a pandemic by the World Health Organization (WHO) on 11 March 2020.
       
Twitter
Chris Macdonald
@Chris_Maccer
Bet it’s not a bad time to be a Jehovah’s Witness knowing that everyone’s gonna be working from home
3:38 PM · Mar 16, 2020·Twitter for Android
   
Twitter
DOGS & PEOPLE
@DOGSPEOPLENL
Replying to @cedarsjwsurvey and @TeamYouTube
If you get a mail with as subject ” ding, dong” , don’t open it it’s from a Jehovah’s witness working from home..
7:00 AM · Mar 22, 2020·Twitter for Android
     
Reddit—Jokes
Posted by u/kowalski655 March 23, 2020
If you receive an email with the title “DING DONG”, do not open it!!!
It’s the Jehovah’s witnesses, working from home
 
Twitter
Apalaceboy61
@Marbar24604616
If you get an email starting ding dong don’t open it, it’s Jehovah’s Witness working from home
6:29 AM · Mar 23, 2020·Twitter for iPhone
       
Facebook
Matt Duda
March 23, 2020 at 8:53 AM ·
If you receive an email with the subject “ding dong”, don’t open it. It’s Jehovah’s Witnesses working from home… 
 
Reddit—Jokes
Posted by u/victor_devito March 23, 2020
If you receive an email with the subject ‘Knock Knock’...
Don’t open it, it’s just Jehovah’s Witnesses working from home!
 
Twitter
Stay Home
@gobaith
Replying to @vocnorth
If you get an email titled Knock Knock, don’t open it. It’s from the Jehovah Witness’s working from home
8:36 AM · Mar 24, 2020·Twitter for iPhone
 
Twitter
G man
@gdog2010_john
If you receive an email with the subject “Ding Dong”, dont open it.
It’s from a jehovah witness who’s working from home.
GIF
11:43 AM · Mar 24, 2020·Twitter for Android
   
Twitter
Tony (Romeo)
@getbent81
WARNING!!!!!
If you get an email or DM saying “knock knock” do NOT open it!!!
It’s a Jehovah witness working from home.
3:35 PM · Mar 25, 2020·Twitter for Android
     
Twitter
LEXX
@lexxstones
If you get an email that sais “KNOCK KNOCK” in the subject line, don’t open it!!! It’s a jehovah’s witness working from home!!
8:01 PM · Apr 11, 2020·Twitter for Android
 
Twitter
Too Tired
@BoredGeekTweets
Covid19 Update:
If you get an email beginning ‘Knock, Knock’ don’t open it!
It’s a Jehovah’s Witness working from home.
5:11 PM · Apr 12, 2020·Twitter for Android