wombat
No, it won't show up at the top, the threads show up in order of originating time.
if it's just one post that is objectionable, select "hide body and subject", and then, yes, it will be hidden in all three forums. the body of the text will read "hidden subject".
if you choose "hide message and replies", the post will completely disappear, even to you, unless you are in administrative mode.
I don't know of any way that you can keep the post intact in the other forums, while hiding it in your own...