An occurrence of one's head coming into contact with a dog, usually with force.
Instances where a headdog is necessary: frustration, drunkenness, humor, etc.
Guy: GAWWD, I AM SEWWWW DRUNK!!!!! *headdog*
Dog: D:<
to be of great quality, top-notch. Stemming from the adjective "heady" when used to describe high-potency trees or weed. head dogs can also be other cool objects, but said with a cocky burnout tone.
hey guy, i picked up some head dogs. lets get lifted.
yo guy, those studded condoms were head dogs. biatch was screaming like a mofo