I wish there was a way to distinguish accidental and on purpose betrayals. More and more lately, I have thrown a plasma grenade, and a team mate will just run on top of it to boot me. Or when there's a big firefight going on, and a team mate gets in the way of my grenade. That really irritates me. I remember one time I was sniping on bone yard, and on a perfection. A team mate spawned in front of me right as i pulled the trigger and i got booted. The betrayal system is really broken in Reach.
I was playing Halo 3 today and i noticed it said " so and so has betrayed you AGAIN, would you like to boot them" but that was after like 4 or 5 times.