My apologies but I can't quite understand what you are trying to say. If you're pertaining to a private chat within DP then use the PM system.
Since you've asked me, I'd still go for the PM system. If I would want to have a more private chat with someone in here. I would do it externally and use other IM such as Skype or Yahoo.
haha good find never knew about it either, doesnt look like many people use it probably because they cant find it lol.