>3rd party as in, I'm sending a message to someone other than you, but I want to refer to something I said to you, or you said to me. It would be confusing if I said "Jay and I discussed ..." and your name was not actually Jay.

Ok, that makes sense. In my case, I don't think there is another Jay around here. And definately not a Renoir. I know there's a Gonzo - can't recall his real name - and I'm sure there are others who informally go by one form of their name, but their given name is the "official" one. The one on file here must be your given name or all hell will break loose.