While screwing a girl in the ass, you pull out and blow the load on the floor. Proceed to rub the girls face in it, while saying "bad dog".
She was being a bitch so I gave her a bad dog.
When involved in doggy style coitus, much like the example of "bad dogs" on youtube, there comes a point when the climax becomes too intense and the 'bad dog' vomits over her back and the surrounding floor/ bed spread/ sidewalk.
I ate some Indian Food for lunch and I bad dogged on Dave
while a girl is sucking your dick, you pull it out and spank her in the face while saying bad dog.
*smack *smack "bad dog"