Most simply, a playa hater is someone who openly criticizes, purposefully attempts to sabotage, or who indulges in any number of other activities/behaviors aimed at someone they consider a playa, or even at playas in general.
The derogatory aspect to the term comes in the idea that the person who's hatin is really only jealous -- they playa hate because they wish they could be as successful, or alternately wishes they could somehow have the playa to themself.
See that there, thats you that is. Meltheaded weapon finder.