Bullying....

Play is apparently highly reinforcing for a great many dogs.  The derailing of play by overly rough behaviors therefore serves as a sufficiently rotten consequence to purge it from most dogs' repertoires.  Likewise, play attempts directed at non-consenting dogs fall flat and so also usually diminish in frequency.  For some dogs, however, roughness and harassment of non-consenting dogs is quite obviously reinforced.  they engage in it all full tilt, with escalating frequency and almost always direct it at designated target dogs.  this can be enormously distressing for target dogs, as well as for humans who witness it.