Nothing exciting; not good or bad. Often an expression used when something good offsets something bad, and you come out even, i.e. in card games where the points for a hand may split evenly.
How was your day?

Eh, you know, kiss your sister. A little up, a little down.
by bc73 December 13, 2010
Stealthiest way of telling someone else to kill themselves.
Kiss your sister = kys = Kill yourself
"Go kiss your sister"
"But I'm an only child"
"You know what I meant"
by Fickt June 25, 2022
I just cleaned the shower, so don't kiss your sister!

no more kissing my sister, you.
(laughs) What? Huh? Hmm? Um, that's an expression for peeing in the shower.
I'm not gonna pee in the shower anymore.
Why? Why doesn't he get to do that? Yeah.
Yeah, that's true.
Why can't I? And why bring it up now? It goes right down the drain.
You know what? Let's all kiss our sister.
by Bexar86 May 11, 2015
Ian you kiss your sisters cat with that mouth: It means when a guy like **Ian** Kisses a cat that belongs to his sister.
Dude 1: Ian you kiss your sisters cat with that mouth?

Ian: You know it!
by #BecomeAPlayerToday March 31, 2021
On June 9th it is considered to be National Kiss Your Step Sister Day. On this day it is highly recommended that you make out with your step sister. Any other day it would be considered incest, but on June 9th it is encouraged!
Person 1: Bro on June 9th you gotta make out with your step sister.

Person 2: Why June 9th?
Person 1: Cuz it’s National Kiss Your Step Sister Day, duh.
by yomommathic April 18, 2020