Historically known as an insturment of cleanliness bestowed upon a dirrty peice of female genitalia, modernly considered a large scale insult bestowed upon the kind of person that would rather eat shit than do something with meaning
Byron would not agree to video tape his sister getting into the shower in the morning even though the rest of his friends thought she was hot; he is a duche bag
"Those douche bags write 'duche bag' and spell 'cunt' with a k," sighed the chagrined old woman, "No wonder society is going straight to fucking hell."
Someone who is known for always saying or doing something that makes you just shake your head and glare at them like they are some kind of retard. Someone with very bad social skills.