KYS

Awwww! A very cute acronym for "Kiss your sister"!

(On a family meeting)
Father (to son) : KYS! It's so cute!
Son : ahem... No.
Father : It stands for "Kiss your sister"!
Son : Ok...

Ur Mommy XY Chrommy

The most ultimate insult. Can create a whole another universe with another one in it.

Person 1 : Ahhh... I hate you so much! No, no, d-don't let it come, n-NO!!!
Person 1 : ur mommy XY chrommy
Person 2 : *Re-creates the universe 100 times*