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

its ya boi
by the peepee poopoo man December 4, 2018

To cut in front of someone. Typically on a bicycle. When a gay fag that watches my little pony porn fucks up harder then gay sex.
by Jimmy Johns let go June 1, 2020

When you and your girl know how its suppose to be done....you can have rough,nasty,sex! Like no others! R-N-S
by Tatum12 December 26, 2020

by icecoldblizzard July 28, 2022
