When you go to stick your head out of the window in the car or what have you and forget to roll the window down... DINK... a thoughtless or careless person who does not think first before acting
A derogatory term which Vietnamese people can reclaim. It comes from the French Vietnamese phrase, "beaucoup dinky dau," which means "very crazy." So, to be a "dink" is to be crazy. It was used to describe to mostly Northern Vietnamese people.