Try and get a kill using only the plasma pistol (no melee).
I swear, it's impossible... I've only got one kill with it and that was against an AFK, and even that took about 20 seconds!
You can get the shields down in a couple of seconds, but then it takes like 20 shots to kill - there's no way that's going to happen against a non-AFK.
So there's my challenge. Kill with the plasma pistol. :)
And if you can do that... try a killing spree w/ PP only.
[Edited on 08.28.2010 1:19 AM PDT]