Thanks Al. I get it now... and your example using WA saying "blame me" is most appropriate
On my mighty Macintosh, while in the post reply screen I can scroll down and right-click the user's name, select Properties and that brings up a window that looks like this:
From there I can copy the post # to the clipboard, then paste it into my reply.
I can't remember if Windows would provide the same functionality, but I would think so.