Ben Trawick-Smith documents the rise of the term “douchebag” to describe generally despicable people:
So let’s put the pieces together. In 1960, when douching was a much more common practice and perhaps more prominent in the public imagination, douchebag would have had a much more disgusting connotation, and likely would have been avoided for this reason. But in the 21st-Century, at a time when many people barely remember what douching was to begin with, it might be taken as a less offensive insult.