This is a chinese slang, which is the initials for “Ni Ma Si Le” which means your mom’s dead. Often used in curses for online/real life arguments.

Got the covid-19 vaccine

The word "NMSL" is a pinyin(Chinese typing/pronunciation system) abbreviation of the Chinese phrase "你妈死了", which translates to "You mother died". The word is used as an insult mainly online and is a part of modern Chinese internet culture. The word gained popularity when mainland Chinese people, mostly teens, circulated government censorship to post pro-China propaganda on western social media and used this word to insult people who said anything negative about China

The abbreviation of "Never Mind the Scandal and Libel".(First time used by a famous Chinese rapper Sun Dog in his famous song "Showtime").