Acronym, used in social media and interpersonal messaging, modeled after the long established 'LMAO' — Laughing My Ass Off.
This exhortation was coined 28 Jul 2002 in the midst of the worldwide COVID-19 pandemic, when surgical or industrial (e.g. N95 or N99) protective masks were widely in use, and mandatory in some jurisdictions or individual shops and public places.