Get them to betray me and then boot them. Me and my friend once booted out whole team in a game of BTB, my greatest trolling achievement so far.
Other fun stuff to do to nooby teammates:
-Stand on top of the Wraith when they are driving so when they fire it betrays you, this also works with the Scorpion but is a bit harder
-Evade in front of their Warthog or Ghost and watch them rage when they splatter you
-Stand in front of their sniper, or if they are hiding stand by them and draw a lot of attention by firing in the air etc.
If they are on the other team I usually just pwn them, however in Doubles on Countdown there is this really good hiding spot on the pipes in that center lift room where me and a friend have hidden from kids a whole game while listening to them rage and accuse us of hacking.