You're Fucking Kidding
That's such a stupid question. YFK right?
YFK stands for Younster Fun Kill.
This means when high leveled players kill players lower than them. They do this because:
1. They are bored.
2. They have a brother or sister PMing them to kill the lower lvl because the brother or sister might want an item from the lower lvl or they might want revenge etc.
3. High levels are sometimes douchebags.
4. The high level might need a refill.(Like pots, arrows, food etc)
5. The high level is annoyed with the lower lvl cuz he might be looting or FCing.
I Kasoy I (lvl 124) YFKs NudyNud12 (lvl 89)
Sickrad2212: You see kasoy yfk that dude?
Tripdsa: Yea, what a YFKer.
Sickrad2212: Probabley for sharks or something.
Suddenly the loot appears on the ground. A few sharks, prayer pots and a dds.
I Kasoy I: Ima YFK or pj you noob tripsda!