etymology- Thought to have first been used during the Dark Ages. Upon surviving an attack from a fire breathing lizard, the last image you would witness before passing out from lack of blood and multiple contusions would be the "Dragon's ass", as it flew away into the night.
When a person is very tired or slow. Often times can be seen in the form of a woman named Brenda dragging her ass on the pavement like a dog with worms. Not a pretty site
"Hey bro, I'm tired"
"Yeah I know. At first I thought you were Brenda but it appears you're just dragging ass"