“LMAO” is a popular initialism for “Laughing My Ass Off.” The 2019–20 coronavirus pandemic required many people to wear face masks.
     
“LMMO (laughing my mask off)” was posted on Twitter by kimba on April 14, 2017. “Y’all I need a new roommate. Abby has gotta go. She’s using phrases like ‘Laughing my mask off. Lmmo’” was posted on Twitter by Maris Martin on June 19, 2017.
     
“We should stop using lol and LMAO and migrate to LMMO (laughing my mask off)” was posted on Twitter by Paul Alexander on March 12, 2020. “LMMO Laughing My Mask Off” was posted on Twitter by Mel later on March 12, 2020.
     
LMFMO (Laughing My Fucking Mask Off) is a similar term.
   
         
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
kimba
@babyfurby1999
LMMO (laughing my mask off)
5:26 PM · Apr 14, 2017·Twitter for iPhone
 
Twitter
Maris Martin
@marisinparis
Y’all I need a new roommate. Abby has gotta go. She’s using phrases like “Laughing my mask off. Lmmo”
9:14 PM · Jun 19, 2017·Twitter for iPhone
 
Twitter
Paul Alexander
@EsportsProducer
We should stop using lol and LMAO and migrate to LMMO (laughing my mask off)
7:31 AM · Mar 12, 2020·Twitter for Android
 
Twitter
Mel
@Mel02738538
Replying to @IanSams
LMMO Laughing My Mask Off
5:38 PM · Mar 12, 2020·Twitter Web App
   
Facebook
Holden Dodge Chrysler Jeep Ram Dover Delaware
March 17, 2020 ·
LMMO, Laughing my mask off ! We are here, we are open for business. Chrysler has just announced unprecedented incentives including 0.0% for 84 months!
   
Twitter
Edward Petracco
@edcolor4u
Replying to @SheaLeparoux
LMMO! (LAUGHING MY MASK OFF!!!)
11:49 AM · Apr 1, 2020 from Clifton, NJ·Twitter for Android
 
Twitter
Dennis
@NoJust1c
A new Acronym
LMMO= Laughing my mask off
8:47 AM · Apr 5, 2020·Twitter for Android
   
Twitter
Dennis
@NoJust1c
#LMMO- Laughing my mask off
8:48 AM · Apr 5, 2020·Twitter for Android
   
Twitter
Mr. Accountability
@theaccountabil4
New acronym: #LMMO
Laughing
My
Mask
Off
It’ll be a thing.
1:39 AM · Apr 6, 2020·Twitter for Android
 
Facebook
Jeff Helbling
May 1, 2020 at 4:09 PM ·
LMMO (laughing my mask off) 😷😂
LMFMO if you’re foul mouthed….
 
Facebook
Triangle Connection
May 4, 2020 at 12:20 PM ·
LMMO: Laughing My Mask Off