Chardin Bleu, also referred to as Chardin Blue, is a wine produced by the Chardin Family in the anime version of Ranma ½. It is only mentioned in the episode Madame St. Paul's Cry for Help, where it is an integral part of the episode's plot.
Chardin Bleu is a strange wine with a highly distinctive deep blue coloration, which contributes to its name. Carrying a "very bad bite", this wine is not produced deliberately and normally kept hidden away, as drinking it causes strange side-effects. The precise effects are not made clear in the series, due to both neccessity for the comedy and by the attitudes of Madame St. Paul, but it seems to induce a state of altered mind beyond that of normal drunkenness.
While partially due to Madame St. Paul's dancing around the issue, Akane and Ranma both mistook the actions of Picolet Chardin II while under its influence to be signs that he had become a vampire; he avoided coming out during the day, evidenced a general dislike of strong light, and possessed little appetite (by the standards of a practitioner of Martial Arts Dining, anyway). Picolet was also extremely amorous under the influence of Chardin Bleu; Madame St. Paul asked Ranma and Akane to come and help her with him by mentioning local girls had "strange marks on their necks" (Picolet had been sneaking out at night and into the chambers of women to "kiss" them, in his own grotesque way), and Picolet ultimately lured Ranma into his tower "nest" to get her drunk so that he could kiss her to his heart's desire as well.
This culminated in Ranma (unintentionally) using the truth of his identity to shock Picolet back to his senses, and Picolet afterwards expressed that he had been unaware of what had happened while he had been drunk on Chardin Bleu.