Anybody who kills their teammate for their weapon deserves to be booted. Though, it's annoying when the betrayer is playing on your box as a guest and you allllllllllllll get booted. Now, for my enjoyment, some truly spectacular kickings of other peoples' asses... by me.
http://www.bungie.net/Stats/GameStats.aspx...46&player=Lubra
http://www.bungie.net/Stats/GameStats.aspx...70&player=Lubra
They were low rankers (as am I, just started and all), but I like my 14 in a row spree.