SIS is an acronym popularized by the Canadian music artist Peaches in her song "Fuck The Pain Away" and it means "Stay in School".
Person 1: Remember the teachings of Peaches: "S-I-S, IUD, Stay in School 'cause it's the best"
Pesron 2: I love Peaches and, you know what, school is really the best!
Pesron 2: I love Peaches and, you know what, school is really the best!
by Max the Mad Cat May 26, 2024
Get the S-I-Smug. ne'er-do-well(s)(s)(s)(s)(s)(s)(s)
wethethhethhethehthehtethethhetettehtehtehtehthehtehthe ne''er-do-do-do-do-do-do-do-do-we'e'e'e'e'e'e'e'e'e'e'e'e'e'e'e'e'el'l'l'l(s)(s)(s)
by Pseudopseudopseudopseudonym May 22, 2024
Get the ne''er-do-do-do-do-do-do-do-do-we'e'e'e'e'e'e'e'e'e'e'e'e'e'e'e'e'el'l'l'l(s)(s)(s)mug. by icecoldblizzard July 28, 2022
Get the A*S*Y*Smug. 
by Angel234IsTheDarkSeraphim April 26, 2025
Get the Canines And Felines Only Eat <<<`s`&`&`&`S`&`&`&`s`>>> Cigarrettes For Iguanas And Bearsmug. by crankyrapper April 8, 2019
Get the S&Smug.