The act of being a douche; an asshole; or backing out of any act of awesomeness.
You: "Dude I'm so drunk, I cant drink anymore!"
Me: "Dude, don't be a Doback."
When a girl is giving you head and then you cum on the girls face or in her mouth. After the act is finished you remove your penis from her mouth and then punch her in the face - causing her to bleed profusely and spew blood from her face like she is breathing fire.
Oh man, after I got a blow job from my girl last night I gave her a dragon punch.