Best place to get this achievement is to go to the bridge.
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That's most likely gonna promote PK boosting which we already have enough of lol.
Just the streak system makes people boost (I've caught a player boosting over 1k PK streak), so imagine if we would implement this.
In overall it's not a bad idea at all, but in my opinion that would promote more PK boosting.
As an achievement, why not, since it's only one time getable.
I'd say it would make a good secret achievement.
its like killing 50 noobs and run when you see someone "good"