douche bag

Douche bag has two meanings.

Literally, it's the rubber bag used to hold liquid for vaginal douching.

As slang, a douchebag is a contemptible person—typically a man who is arrogant, obnoxious, or aggressively unpleasant: That douchebag cut in line.

The insult suggests someone both offensive and oblivious to their own odiousness.