A portmanteau of "touché" and "douche." When a person delivers a clever and cutting remark in response to another person's argument, the latter may respond with "Douché!" as acknowledgment of a good yet decidedly douchey response.
Dean: Where did I go wrong? How is my own brother drinking demon blood without me noticing?
Sam: Maybe if you stopped crying at every scenic road, you'd have noticed.
Dean: ... Douché.