Douche bag, douchebag, or simply douche, is considered to be a pejorative term, referring to an arrogant or obnoxious person. The slang usage of the term originated in the 1960s.
[From wikipedia]
You can also google ‘online slang dictionary’ or ‘urban’ dictionary & get more “descriptive” definitions.
I thought the term had something to do with female hygiene.