If you really want some go to the regular sleeper and they should have it (and aren't you toatally entitled to have any coffee/juice, etc from any sleeper you want if you're a sleeper pax?).
Yes, you are entitled, but some sleeping car attendants can get very upset when they see people doing that. I suspect that one reason that they get upset is the fact that it's often an indication that their counterpart in the other sleeper isn't doing his/her job catering to their charges.
I have to agree with Alan. Though "upset" is an understatement.
In the Viewliners, it use to be the "norm" to find that in your car that either the coffee pot didn't work, or there simply wasn't one. The SCA would apologize, and suggest using the coffee pot in the next Viewliner. I still remember attempting to do that, and getting
verbally harassed and chased away by that Viewliner's SCA.
I would go back, tell my SCA about it, and he would then go to the dining car to fetch me some coffee. That would also make me feel even more uncomfortable since I am perfectly capable of walking to the dining car myself.