An acronym that stands for "Kill yourself" which is mostly used by toxic people on the internet,
they use this because they are mad or just use this for no reason.
The phrase “kys” means “kill yourself”, it’s a very.. mean thing to say and could cut deep, sooo don’t say it. And if u have been told that it’s okay just ignore them (I have ingnored them and honestly it doesn’t bother me anymore :) )