God, it's very irritating and unfair when you're the boss and you instantly get backstabbed. You could have been waiting for hours to be the boss!
The new system Slayer uses makes it less likely you'll have to wait for an absurd amount of time before becoming the boss. Also, a backstab means the amount of time until you get to be the boss is shortened by the duration of the rest of the current round.
They are also totally avoidable. The only time I've ever been backstabbed is when someone used the horse ray on me and jumped on me. Even then, I was playing as Demonhead SuperRiddler, so the damage was minimal and I soon turned back into normal, killing the player in a fiery explosion at the same time.