today i did a double post, tried to delete it using the "edit/delete" button at the bottom right of the post, but the edit screen showed up, but how does one delete the complete post, so it doesn't show?
Only moderators/super moderators/administrators can delete posts.
You can edit your duplicated post to say "duplicate post" or you can ask the moderator of that forum (or super moderator or admin) to delete the post for you.
THe delete is disabled so someone can't post something insulting and then delete it after doing it. Even if the words or pic is edited, the post still remains in the same spot to prove that something was there.
You can ask the moderator of the section, or I'll be glad to do it in whatever section it's in. I know Z loves the look of a clean forum, lol. And yes, the reason the feature was disabled, was so that someone couldn't post something bad, then delete it and get away with it later.