The act of just writing k in a text/im. People generally don't like responding to such a small answer thus being k'd generally ends the conversation. If you are the one being k'd, you should assume the person that k'd you is either very mad at you, or very pissy.
1: Hey, are you ok? You seem upset.
2: I don't wanna talk about it.
1: Well I'm here if you do
1: *thinks to them self* Wow, I can't believe he just k'd me! I'm not answering that!
When you do a really good job on something but it ends up not being important and a waste of time.
1: Dude I totally aced that quiz!
2: You know it was just a practice quiz, it doesn't count for marks...
1: What?! Man, I was totally legit for shit!
When someone purposely gives you a huge amount notifications on facebook.
Ugh, 47 notifications from Lucas? I gotta tell him to stop notifittacking me!