I was playing when a red guy spawned next to me. At the blue base. So when I shoot him, I die. Turns out that I am that red guy, and this guy. This red guy follows me everywhere, copying my movement. He shoots the same way as me, looks the same way. And whenever this guy named Worm said something, it came up on my guy.
I would also randomly switch to my knife, or suddenly have a minigun instead of an MP5 in the middle of a fight.

This is a rare, though inexplicable bug. Just exit and rejoin.

i had this once on a zombie server

somtimes killing yourself with yourself (am i making sense?) fixes it too

Today I came on a server, and spawned on this red guy, and suddenly I was him. My camera was centered on him, and I controlled some of his movements, and he controlled some of them. My guy just ran behind us. It was REALLY strange.