In Security they say that the biggest threat is always insiders.  People that have access, or people that are generally not supposed to be a threat can always be a big threat.  A lot of times its ignorance some times its an inside job/attack.
Todays Crap Kill comes to you pertaining to this context.  

Sometimes it doesnt matter how good you are or how good you are doing.  You can shoot an enemy and then assist in killing another.  You can take bullets for your teammates.  These things dont always matter.  They will still shoot you!
Heir Muellah aka Dick walks up on Jeef and puts him down even while he is patching himself.