A growingly popular abbreviation for the phrase sorry not sorry. It is usually said in a sarcastic way, and almost never used to genuinely mean sorry. SARS is pronounced with emphasis on both the first and last s.
"Hey Saylor, are you coming out with us tonight?"
"Sorry Ab, I'll probably have a date tonight, SARS"
This is a correct use of SARS because Saylor is not serious, and won't have a date. She says this to her friends to make her seem superior, and since she says SARS they understand that she will probably come.