"Janitor" was a janitor working in the motel the T-800 was using as a safe-house.
The T-800 was looking through Sarah Connor's diary to find a location while a Janitor started knocking on its rooms door because he noticed a foul smell coming from the T-800s decaying living tissue. He asked the machine "Hey buddy, got a dead cat in there or what?" while the T-800 responded with a "Fuck you, asshole." He then walked away with his mop cart.