I found these origins http://dialectblog.com/2011/07/01/on-the-evolution-of-douchebag/ and http://askville.amazon.com/origin-insult-douchebag/AnswerViewer.do?requestId=12541998

You bet James!!! congratulations!

The word douche comes from French, which means shower. In English, however, the term is specifically describes thoroughly washing the inside of the vagina. It is often considered an unhealthy process. In pharmacies, douche kits can be bought. I assume they include a bag or something. But anyway, it's basically describing a bag of dirty water that was used to wash a vagina. Although it sounds quite gross, "douche bag" is not incredibly severe. It's often used to describe a person who is very 骄傲 (which I've somehow momentarily forgotten how to say in English) and is overall a total jerk. I'm guessing you found the weird on my WeChat, huh? :D

good to know` thank you

"Tool" can also be used as an insult roughly equivalent to 'Douchebag'. As in "That guy is a real tool"