Killjoy

Killjoy is a medal awarded in Halo 3 Multiplayer To obtain this medal you must kill somebody who is on a Killing Spree. You can also kill someone who is achieving a streak greater than this, such as a killing frenzy, etc. in order to earn this medal. It is represented by an octagon with a crossed-out smiley. This medal is very random as you don't know which players are on killing sprees, unless of course, he has killed you or your team multiple times without dying.