MW3? Why do teammates knife you when you block a door in call of duty?

I was playing call of duty and I stopped in a door cause I had to pee, so I left, and when I came back there were a bunch of teammates knifing me. I have seen this happen several times before? What do they think stabbing a teammate will do?
Update: I understand that they want me to move, but if someone was deliberately trying to piss them off, why would they move just cause they knife him?
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