Its proper definition of douche is the introduction of of a fluid into the vagina for medical or hygienic reasons. Not being an enjoyable process, its derivatives are usually meant to insult. Terms such as shower pocket, douchebag, d-bag, DB, doucherama, doucher, douche turd, douchington, or simply douche are not uncommon.
"that cop gave me a ticket for only going 5mph over the limit, what a douche!"
"I'm trying to impress these people I'm taking you to meet, so don't be a d-bag or anything, ok?"