if you delete a comment and you are asked if you want to delete and bann user. does the user get told this? if so in what way?

No, they don't get told.  you just dissapear off their friend list.  I tested this as I wanted to do a clear out without hurting feelings so I banned a friend and then asked her.  Only thing is, if you block them, then re-friend them, you can't block again for 48 hours.
With regards to the comment, your post will just dissapear but if anyone has commented on your post, it'll look weird and they might find out that way.
TBH, if someone had annoyed me that much, I wouldn't care whether they knew or not!

Cracar, thanks for that.