A true dew-rag (this is the correct spelling) is made from one piece of cloth that is cut into a triangle and worn over the head and tied at the back of the head. It must also either be made by an Infantryman or Infantry Veteran or worn by an Infantryman or Infantry Veteran or it is not a dew-rag, it would be a skull cap.
Dew-rags are worn to protect the wearers head from dew collecting in the hair after sleeping outdoors, to use as a sweat rag, to use as a cleaning rag, to provide some cushioning from the helmet liner and to help prevent helmet creases from forming in the hair. Infantry Veterans may wear them to show honorable service. Others may wear them to show support for the Infantryman or Infantry Veteran who made it.
That stuffed animal that's all torn up and dirty that nobody touches because the family dog spends all day alternating between chewing it and humping it.
"I know you want to play with Fluffy but you might want to get that out of your mouth, it's his Scooby Dew rag!!