It is a bit of a play on words. Doux is the sweetest of all champagnes, which I am partial to. I do like to serve my champagne with a pun or two as well. Hence my command of the somewhat misspoken phrase. If you're talking about a smooth talker and a phrase people actually use, I do believe its is beau-parleur. And contrary to what LH might suggest, plenty of women won't go for this type of approach regardless of other attributes. It tends to be very hit or miss and quickly so. Quite a few women prefer the demi sec man to the doux.
